So many things:
1) the main thing this thread points out is how weak the field for expansion is. There is BYU at #1, but only for the BIG 12. No one else wants them. After that Houston is #2, but only based on recent performance. What happens when their coach leaves for UT or another long established program? Memphis? Cinnci? UConn? USF? UCF? What do any current Big12 fans care about any of these schools? Or any other conference for that matter?
2) The driving force behind Big12 expansion was the Oklahoma President. He told the conference that either they expand or OU was gone. The vote changed just hours (or less) before the vote was taken. In fact, just before the vote was taken, there was a news story that the Big12 was going to pass on expansion yet again. If the Big12 does expand, OU will be obligated to stay.
3) As far as expansion of the other P5 conferences there are no generalizations. There is not one conference that has any interest in expansion just because of a popular notion of 16 teams. Not one conference will dilute current members share of the pie just to get to some number, especially with the paucity of value adding candidates. Of all the teams out there who can add value to any conference, there are ND and UT. Period.
4) No one has mentioned any reason why the Pac12 should expand. Maybe because they want to reduce their members' share of conference income? Maybe because they all want to play in Boise every other year? Maybe because they want another team with lousy academics in a conference that is mostly very highly regarded academic institutions? IMO, the Pac12 is the least likely to expand.
5) The SEC would love to have UT (as would everyone) and would be happy to take OU as a partner. Who else makes sense for the SEC? Everyone else is dilutive to members' income.
6) The Big10 is in the same boat. Name the schools beside ND and UT that will increase members' income. Anyone? OK. Maybe UVA solidifies the MD/VA/DC market. Maybe GaTech adds a piece of the Atlanta market. Is that enough? Will the Big10 wait forever for ND? Now that Big10 members will be making more than ND perhaps they will have a change of heart. Probably not. ND likes the ACC schedule a lot better than the BIG schedule. Can you see ND in the BIG East?
7) ACC. Second most likely conference to expand, but only if ND joins as a full member. Ironically, UConn is likely in the same position as RU was a few years ago; tied to ND joining the BIG (for UConn it is the ACC), before the BIG gave up and settled on UMD.
8) Isn't it amazing how the conversation has changed. Just a few months ago these discussions on expansion focused on existing P5 teams changing conferences. Clemson and FSU to the SEC, etc. Now that possibility isn't even mentioned. Unfortunately, until a lot of people get over the idea that there is some universal force that will make all the conferences take bad teams and lose a lot of money just to get to what seems to be the magical number of 16, these conversations are doomed to continue.