...However, no team already in a BCS conference wants to join, and outside of Arkansas, the Big XII doesn't want to go outside its footprint. Which two teams in the poll above are most likely to join?
Well, with the restrictions of NO BCS schools outside of Arkansas:
To me the obvious choices are
Arkansas is a flagship with a UT friendly worldview and gives the Big XII Arkansas's markets and Memphis.
Utah is a flagship in a growing state, is a strong academic school, and gives a solid market in SLC.
With the restrictions of NO BCS schools and not outside of the current footprint...that's a lot harder. I think in that scenario you either look for value or for a defensive position.
The big XII already owns their footprint and are athletically superior to any team within the footprint. In terms of value would be academic.
Adding Rice and division II Washington University would make academic sense, but not athletic sense.
Adding schools defensively would be to prevent schools for encroaching on Big XII territory.
Maybe Houston to block possible SEC expansion and CSU to take full ownership of the Denver market and force the MWC westward.
Of the schools on your list, I'd take UALR to expand the footprint and CSU looks the best fit. They are jjust as viable as K state.