There are 10 conferences.

From the Group of 5, there are 3 leagues where 75%+ of the members have been playing the highest level of college football since D-1A was created in 1978:

MAC
MWC
American

Out of the SunBelt and C-USA combined, only Rice, Southern Miss, UTEP, NM St and ULaLa have been playing the top level of college football continuously since 1978. You aren't losing much in the history and tradition of college football if those 2 leagues are not invited.

Accordingly, I hope the MAC, MWC and American (along with BYU and Army) band together and demand to be grandfathered in based on history, assuming we are willing to commit to the new Divisional structure.

For example, currently schools must sponsor at least 14 sports to be a FBS football program.  I can see that number jumping to 20 or more to stay upper division football.  See this article.  

Of the 65 teams in the Power 5 conferences, 23 sponsor 16-19 sports.  26 sponsor 20-23 sports.  And only 16 sponsor 24+ sports.