Unless the CFP payout expands beyond $10 million per conference then I don't see the Sun Belt expanding. They're at the peak teams/$ compared to the MAC and CUSA. They have no reason to expand now that they can have their conference championship game, $10 million CFP payout, and remain at 10 teams.
CUSA is a chaser of markets. KSU might be up their alley. They can get that ATL-Charlotte rivalry going.