It would be a huge logistical nightmare for college athletics. The biggest thing about promotion and relegation is that every team plays every other team twice, home and away, so they have a completely balanced schedule. I don’t know how you do that especially in football.
But you could do a “two seasons” approach where the top two teams in each conference move on to the promotion tournament (or national championship if you are at the highest level) and the bottom two teams move on to the relegation tournament. In basketball that could just be your NCAA tournament and NIT respectively.
But if you’re going to do that you’d have to eliminate the OOC and every conference would have to have a completely balanced schedule.
I also can’t ever imagine this happening because the P4 would never elect to exposure their bottom feeders to relegation or allow in schools they deem as unworthy into their ranks. You’d also have to split up into something like 7 or 8 divisions so Boston College isn’t fighting relegation against NCA&T or something.
Oh, and I would prefer groups and round robin first round for promotion rather than single elimination. Give every team 3 games to make their case before bowing out.
And then for relegation a shortened season where everyone plays home and home and the bottom X teams go down, every else stays up.
Edit: maybe split D1 into three tiers, 8 conferences each. And then maybe you could do top 3/bottom 3 and so 24 teams for each “clausura” — to steal Liga MX’s name.