My guess if the SEC does expand they're first going to look at FSU and Miami and add in 2/3 of Virginia Tech, Georgia Tech, or Clemson, and they'll have their 16. I'm guessing if that happens the Big East and ACC combine to get a conference that could still be considered an AQ. Wouldn't be surprised in that situation of the strong Basketball schools make up a conference for them, or what the Big East was proposing an all Catholic conference or Basketball only schools form their own conference.
In that situation the Big 10 would add ND, NU, MU, Rutgers, Pittsburgh, or another Big East team.
The Pac 16 includes all the Big XII schools besides Baylor (who would really benefit from being in a non-BCS conference athletically, probably not financially). Baylor and Iowa State go to the MWC, but I could see Kansas and K-State going to Conference USA (a better basketball conference), or they could go along with Baylor and Iowa State to the MWC. Who when they bring in Boise State will enhance their profile to become an AQ conference. (MWC could also poach Houston for the 16th team) I don't know the MWC is awfully close to being an AQ, and they've at least been as strong as the Big East in recent years.
So for the AQ conferences will be the Pac-16, MWC, Big 10(+6), an ACC/Big East merger, and the SEC. What the BCS does after everything settles, I don't know, but it's very likely some form of playoff comes from it.