I do think that Air Jamaica might join eventually, and this would supplement SkyTeam's large Caribbean service. As for other carriers, Avianca and TAM are the only real possibilities I see. TAM is a partner of Air France (to my knowledge), but also of AA and I think BA (might not be though), so that might lead to OneWorld.
For Emirates, as badly as I would like to see them enter SkyTeam, they have publicly stated that they don't intend on joining an alliance. Now, this could be just PR and they are discussing the possibility of joining an alliance in the backroom at this moment, but I would tend to doubt it.
For Thai, I honestly think that they will stay in Star. After reading this month's Airways article on Star, it clearly says that Thai could have vetoed SQ's application for Star, but they didn't. However, if AF does buy the government's stake in Thai, I wouldn't be surprised to see Thai change ship. Remember, Air France has money and is making money right now, and it is in a better shape than Lufthansa/BMI/Austrian Group to buy into it.
As for another US partner for the alliances...it could be possible. However, a merger might still be the more likely option. For America West or US Airways joining, I doubt it. These two airlines don't have the financial strength to help out in an alliance, but if they rebound (I think AmWest has a shot, US Airways a really small shot), they could become nice supplements to an alliance.