Assuming that a 1-person switch occurs...Does anyone know enough about the European version(s) to know if that person gets any sort of immunity consideration from that first TC?
If the switchee plays it right, it's actually a position of great power because the switchee has the ultimate bargaining chip -- the voting history of the other tribe. If I were the person switched, I would promise my new tribemates the complete voting history of my original tribe...after the merge takes place.
As for who gets switched, if the tribes choose which one they wanted to dismiss, I think that it would be Theresa and MamaKim. The Mallrats know they would still have a 4-2 advantage, so they would keep Frank for challenge strength, as well as the hope of making him squirm about being outnumbered. The Boron have already come to terms with letting MamaKim go, and she has been a liability in challenges, so they would be willing to cut her loose.
It would be so fun to see Theresa seal the doom of Lindsay and Silas by telling the Boran about their previous votes.