Oregon State, UF, FSU & UVA are all virtual locks to get national seeds.
Ole Miss, ULaLa, Indiana, Miami, South Carolina, OkStU & TCU are all strong candidates for the other 4 national seeds. How those teams do in the conference tournaments will dictate what happens.
That's 11 teams (above) that will undoubtedly host a Regional. Add Cal Poly & Washington to that list (on merit and to get some Western US host sites).
The other 3 host sites should come from this list:
LSU or Vandy (depending on SEC Tourney outcomes)
Louisville or Houston (depending on the AAC tourney)
Rice (would have to have a miserable tourney to get leapfrogged, IMO)
Texas (has to win the Big 12 tourney AND needs others to lose)