re: Players sitting out for bowl games will force playoff expansion to 8, 12 or even 16 teams.

Nope it won't. All the powers that be said the bcs would run it's contract and no one beleived them but it did. Same thing here. They may tweek it some after 2025, maybe go to six but I doubt it. It won't be going to eight though. You will have to find some other way to make besides letting undeserving teams in.