Though my preference would be for the Krystle/Rita swap to take place prior to the Carringtons leaving for Moldavia with Rita being killed in the coup, an alternate would be:
Sammy Jo befriends Rita hoping she can find a way to use her resemblance to Krytstle to get her inheritance. Sammy Jo humors Rita by listening to tales of her illustrious career: "and in this film I was attacked by giant radioactive ants!" Joel gets involved and the swap happens shortly after the Carrington's return from Moldavia - not accidentally, no karate chop to the neck. Rita does her best to impersonate Krystle but family members begin to comment to one another that there's something off about Krystle.
After undoing the trust that Daniel left to Sammy Jo (letting Sammy Jo have access to her entire inheritance) "Krystle" begins siphoning money out of Krystle's bank accounts. "Krystle" makes large credit card purchase and then tries to return the items for cash. It's only after Blake becomes aware of the shady money dealings that Blake confronts "Krystle". "Krystle" tries to talk her way out of it when Blake asks if maybe her behavior is the result of the emotional trauma she experienced during the coup in Moldavia; "Krystle" goes along with this, even agreeing to see a psychiatrist. Joel realizes it's time to switch Krystle and Rita back and get out of town.
During the time she's been Joel's captive (not at Delta Rho - nothing to connect it to Sammy Jo) Krystle has wondered who would hate her enough to put her through this ordeal. She can only think of one person: Alexis. When Krystle asks Joel if Alexis is responsible for her kidnapping he is vague at first but he eventually lets Krystle believe she's discovered the truth.
Krystle is released and Joel and Rita skip town with the money they've managed to get (not that much - at least to a Carrington). Krystle tells Blake of her ordeal and the horrible woman who impersonated her. Blake is convinced Krystle has suffered a complete breakdown. The psychiatrist (whom Krystle insists she has never met before) examines Krystle; he believes she is suffering from a delusion but doesn't diagnose her as clinically insane - she does not need to be committed. Blake gathers the family together and urges them to be patient with Krystle during this difficult time.
The Carringtons are invited to a black tie gala. Blake asks Steven to keep Alexis from attending the gala to avoid upsetting Krystle; Alexis has plans out of town so it shouldn't be a problem. Blake and Krystle are enjoying themselves at the gala when Alexis arrives unexpectedly: "I changed my mind". Krystle becomes upset and, seeing an opportunity, Alexis provokes her. Krystle loses her temper and violently lashes out at Alexis; the paparazzi's camera bulbs begin to flash. Alexis (despite Steven and Amanda's pleas not to) presses charges against Krystle who is charged with assault. At her arraignment Krystle is remorseful and all appears to be going well until the judge asks what would make such a poised and graceful lady behave in such a way. Krystle tells of her kidnapping and replacement with a doppleganger. The D.A. requests a psychiatric evaluation and the judge approves. Krystle fails the evaluation and is sent to a psychiatric facility pending her trial.
First off:


Second off...
Sammy Jo befriends Rita hoping she can find a way to use her resemblance to Krytstle to get her inheritance. Sammy Jo humors Rita by listening to tales of her illustrious career: "and in this film I was attacked by giant radioactive ants!"
Great reference to Joan Collins' previous work.
Yes, Adam should definitely get involved. In fact, he's the one who figures out where to keep Krystle, and like I've suggested before, uses "Krystle" to help him convince Blake of doing certain business ventures (not sure what yet).
the swap happens shortly after the Carrington's return from Moldavia - not accidentally, no karate chop to the neck.
Since you mentioned that Krystle knows she was being impersonated, how did she find that out? Would you keep in Krystle walking in on Rita? Or would Krystle simply catch a glimpse of Rita as the former is being chloroformed by Joel?
Also, you say shortly after the family returns from Moldavia... but what about Fallon's return? When would (or should) that happen in regards to the whole doppelganger incident?
Rita does her best to impersonate Krystle but family members begin to comment to one another that there's something off about Krystle.
I've talked about this in a different thread before: as Sammy Jo and Joel are prepping Rita to make her look like Krystle, SJ complains that Rita looks all wrong. "She looked more like Aunt Krystle when she had red hair and heavy makeup!"
That makes Joel realize that they can't make Rita look exactly like Krystle, otherwise Rita'll just look like a cheap knockoff, and nobody will be fooled. At this, Sammy Jo is ready to give up, but Joel points out they simply need to make Krystle look like Rita as well.
So Sammy Jo convinces Auntie Krystle to come and have a "day of beauty" with her niece, who charms her aunt into getting a new hairstyle and makeup job. Rita later gets the same, and both Joel and Sammy Jo agree that *now* the two women look identical.
The family sees the real Krystle with her new look, and compliment her, with Steven remarking, "You look like a new woman!" (Haha.

)
However, when Rita shows up, Blake does a double-take when he sees her. Obviously nervous but managing to cover it up with a smile, Rita says to her "husband", "Still not used to the new hairstyle, darling?"
"Er... no, I suppose not," responds Blake. He smiles and shrugs, dismissing any suspicion.
But yes, the rest of the family begins to agree that there's "something off" about Krystle.
After undoing the trust that Daniel left to Sammy Jo (letting Sammy Jo have access to her entire inheritance) "Krystle" begins siphoning money out of Krystle's bank accounts. "Krystle" makes large credit card purchase and then tries to return the items for cash. It's only after Blake becomes aware of the shady money dealings that Blake confronts "Krystle". "Krystle" tries to talk her way out of it when Blake asks if maybe her behavior is the result of the emotional trauma she experienced during the coup in Moldavia; "Krystle" goes along with this, even agreeing to see a psychiatrist. Joel realizes it's time to switch Krystle and Rita back and get out of town.
Wow. You actually made the bad guys smart. Bravo.
During the time she's been Joel's captive (not at Delta Rho - nothing to connect it to Sammy Jo) Krystle has wondered who would hate her enough to put her through this ordeal. She can only think of one person: Alexis. When Krystle asks Joel if Alexis is responsible for her kidnapping he is vague at first but he eventually lets Krystle believe she's discovered the truth.
Excellent.

I'd have it so that at first, Krystle believes she's being held captive by the guerrillas from Moldavia, and Joel lets her believe it. But after listening carefully to Joel, Krystle realizes his accent is fake. He can't be one of the guerrillas. She confronts him, but he won't say anything. Krystle is forced to arrive to conclusions herself, and just as you said, she can only think of one person who'd do this to her: Alexis.
Krystle is released and Joel and Rita skip town
I'd still try to keep the catfight. I suppose there's a miscommunication that happens between Joel and Rita so that the latter accidentally goes where Krystle is being kept. Krystle attacks her double, and the fight commences. Joel overhears the ruckus, and grabs more chloroform. Right after Krystle defeats Rita with a mean right hook, Joel jumps on her and knocks her out. Joel places Krystle in her own car and drives it somewhere, while Rita follows in Joel's car. They put Krystle behind the wheel, and drive off. Krystle is awakened when a cop knocks on her window.
Krystle tells Blake of her ordeal and the horrible woman who impersonated her. Blake is convinced Krystle has suffered a complete breakdown. The psychiatrist (whom Krystle insists she has never met before) examines Krystle; he believes she is suffering from a delusion but doesn't diagnose her as clinically insane - she does not need to be committed. Blake gathers the family together and urges them to be patient with Krystle during this difficult time.
Hah. I love it.
The Carringtons are invited to a black tie gala. Blake asks Steven to keep Alexis from attending the gala to avoid upsetting Krystle; Alexis has plans out of town so it shouldn't be a problem. Blake and Krystle are enjoying themselves at the gala when Alexis arrives unexpectedly: "I changed my mind". Krystle becomes upset and, seeing an opportunity, Alexis provokes her. Krystle loses her temper and violently lashes out at Alexis; the paparazzi's camera bulbs begin to flash.
YES! A grand Krystle/Alexis catfight that Season 6 never had (the mudslide never really counted; though I would keep that in too).
Alexis (despite Steven and Amanda's pleas not to) presses charges against Krystle who is charged with assault. At her arraignment Krystle is remorseful and all appears to be going well until the judge asks what would make such a poised and graceful lady behave in such a way. Krystle tells of her kidnapping and replacement with a doppleganger. The D.A. requests a psychiatric evaluation and the judge approves. Krystle fails the evaluation and is sent to a psychiatric facility pending her trial.
How would Krystle fail the evaluation, though? Especially if the previous psychiatrist said Krystle did not need to be committed? Although, I'd be tempted to allow that to happen because...
Basically this should have been the back bone of season 6. I can see an episode cliff hanger with Krystle stood to hear the psychiatric evaluation results then collapsing as she's all but declared insane and committed to a psychiatric ward as the swirly Dynastic music swells to dramatic effect around her. Alexis looking shocked but pleased. Blake looking terrified and Amanda and Steven consoling each other in this horror. The final scene of the episode a sort of homage to the reactions of the cast when Alexis took the stand at Blake's trial.
...this actually does sound amazing.
And then the big question will be: what is Sammy Jo going to do, since she's the only other person who knows the truth. Or maybe Adam too.
Actually, I thought of a possible way for Krystle to get out of this mess: in the past, I suggested that there should be more physical differences between Krystle and Rita aside from their hair, nose and accent. Rita should have gray eyes which she disguises with colored contacts; Rita should also have a tattoo on her right shoulder-blade that she never thought to get rid of beforehand and always had to keep covered up while in disguise.
However, Blake caught a glimpse of the tattoo once and was thunderstruck that his wife would get such a thing. Rita claimed that Sammy Jo talked her into getting one "because it was fun!" Later, Blake sees the real Krystle with her back exposed as she undresses in front of him, and he sees the tattoo is gone. He asks her about it, and she of course has no idea what he's talking about. Blake then goes to Sammy Jo to ask if she ever convinced her aunt to get a tattoo.
Sammy Jo answers no, and Blake realizes that Krystle *must* have been telling the truth after all! Blake describes Rita's tattoo to Sammy Jo to make sure, and SJ realizes she has a chance to help her aunt and ease her own guilt. She confirms that she never convinced Krystle of such an act, but she also "remembers" catching a glimpse of the tattoo when she and "Krystle" were conversing in her aunt's room and "Krystle" changed into another top.
I know it's not much, but maybe other things that the rest of the family remembers come up, and together they're all able to offer up enough proof that Krystle indeed had been kidnapped and replaced by an impostor.
And this is what sparks the fight between Blake and Alexis: not Alexis suddenly falling back in love with Blake, but Blake taking Krystle's side and believing that Alexis was behind the whole thing. Alexis is furious and outraged, insisting she is innocent, but Blake just calls her a liar... and a few other colorful things. He also says that, while he can't prove Alexis did it ("Just like how I can't prove you killed my baby!"), he will be imposing a restraining order on her so that she is legally barred from coming near the Carrington mansion.
Practically foaming at the mouth, Alexis goes on a tirade about being cut off from her grandchildren - sorry, her "children's children!" - and how Krystle is mentally ill and needs to be locked up, and after Blake storms out, Alexis declares she'll destroy him once and for all... and goes to Australia to bring back Ben.