I would think that there are perhaps 2 members who have the most potential to move on (neither is Ohio in my mind). There may be others that I’m missing though based on market size, etc.
I presume you're meaning NIU and Buffalo. I wouldn't sell Toledo short in this regard. They have a solid football program year in and year out and their b-ball program is always one to be reckoned with. Now that the NIT doesn't automatically take conference champs that don't win their conference tourney, the MAC is largely going to be a one-bid post-season b-ball conference. This might schools like Toledo not only attractive to a conference like the American, but make the schools more willing to move on.
But a drawback for the MAC schools is that the current thinking among larger conferences is to have more of a presence in "football havens," mainly Texas and Florida. That's one reason why SMU -- instead of Oregon St and/or Wash St -- is now in the ACC. And it's why teams like North Texas, UTSA, Rice, and FAU were involved in the last reshuffling of conferences. Most conference heads don't consider Ohio, Michigan, Illinois, Indiana and New York to be football havens.