At this point I'm expecting the split at the FBS level to occur around 2031 (I believe when the next round of contracts occur). It will be:
BIG10, SEC, BIG12, ACC, Notre Dame and perhaps a handful of other schools who are willing to throw the $$ into it. There are 68 schools in the above Conferences so add 4 more to get to 72, taking TV value, history etc. into account (Boise State, Wazzu, OSU + UCONN)
The next level would be all the current G5 schools plus the upper echelons of FCS, call this D-1AA:
MWC, Sunbelt, CUSA, MAC, AAC
This gives you 65 teams (assuming Davis gets an FBS invite to the MWC) and THIS is the level we should be at. Both Montanas, Dakota States and a few more who want to move up (Tarleton, SAC State etc.)
Both could adopt the format similar to the NFL, have 8 Conferences of 9 teams in each and make them as regional as possible. Granted I'm just theorizing here but unfortunately whatever makes the most $$ is all that's going to matter.