I vote for #3 and here's why:

In S5, we had the tribes given the option of switching teams, and while plenty thought about it, no one did it. Then there was the whole non-merge, which really threw the teams for a loop. In S6, the big hype has been men v. women. Why mess with it now? And everything so far has been pretty fair between the 2 tribes (here we sit at 6 v. 6).

So let's say that MB has them pick an ambassador from each team. The girls pick Jenna and the guys pick Dave. Although I don't find any of the women particularly beautiful at this time, for the sake of argument, I think Jenna can probably "work it" better than any of the rest, and maybe Alex's injury prevents him from going, leaving Dave as second choice. The two meet thinking "plans for the merge." Only MB turns the tables on them and has them live together with no merge. Think about how much sexual tension there has been so far. Now picture them living together, but still competing against each other.

I just think it's too soon to merge, and there's no need to swap.