136 teams (i assume this is current D1) split in half 68/68

Upper and lower tiers with relegation and promotion for all schools (no exceptions as OP noted)

Something like a 24-team playoff

An algorithm based ranking system for allocation of funds. No human inputs. Rules for algo ranking are established at the start of the season and agreed to by all participating schools

BYU is in the upper to begin.

I actually think it would be quite fun. The matchups would be better than current. Get rid of FCS and G5 games! Have a pre season scrimmage if you want.