I just think you have to be careful adding too many teams, and I don't think the conferences would agree to too many anyway. I really believe you've got to keep a bowl system of some sort. To me K-State is living proof that moving up through minor/medium bowl games can build a program, granted I think there are too many bowl games now.
I could see a system where the Sat. before January 1st (a week out, more when Jan 1 is in the middle of the week) you have the 4 opening games on college campuses as sort of the opening of medium or better bowl week. You would have some minor bowls like for the Sun Belt, MAC level teams before that. Then in between, ESPN still has their bowl week with decent games (Holiday Level) for teams that didn't make the 8 team playoff. Then January 1st would be for a couple top level bowl games (teams that finished 9-12ish could match-up) at former BCS sites, and then the semi finals later that day at the other 2 former BCS sites. Then a week later you have the Championship game at one of those sites. The current 4 big bowls rotate the two "big/leftover" bowl games and semis with one of those 4 getting the Champ game a week later, similar to what they do now. This keeps a bit of the flavor of the bowl system, but adds a legitimate playoff system.
:2cents: