This year went perfectly for a 4 team playoff, but most years aren't going to work out that way. Wait until a 2-loss SEC champ or a 2-loss B1G champ gets left out of the picture. They'll get there eventually . There's too much money in 8 teams for them to ignore it too long.
The BCS was hunky-dory until we had a rematch of SEC teams and people realized there was too much bias in the system.
The power broker of college football is ESPN. I believe eventually there will be an 8 team playoff. Too much money (Too many commercials that could have been sold) left on the table.