I think it might be better if the playoff separated from the current bowls. A little like when the BCS decided to create a new "BCS National Title" that rotated sites rather than one of the bowls being the national title game.
One problem with the current system is that the semifinal bowls end up losing their role as a destination. The whole point of the bowls is to cap off the season. For the winning team, the "prestigious" bowl ends up becoming just another step on the way to the title. The other issue is the rotation of the NY6 reintroduced the problem the BCS had before the introduction of the championship as its own bowl game. Every three years, the Rose Bowl isn't Big Ten/Pac 12, the Sugar Bowl isn't SEC/Big XII, and the Orange Bowl misses an ACC team. Bowls have prestige because of tradition, and that tradition is usually based on conference tie-ins.
Separate the semis into other bowls. That could be the BCS model of an additional game at a current bowl site, or make those bid sites like the national championship that change each year. Another option is to go to a Final Four model with everything at the same site, but no NFL team is going to want three extra games on their field in seven days. Plus, these games have enough interest to fill a stadium for one game, so either you'd have to play the games day/night and empty it between games, or play them a day apart and give a team an extra day of rest/scouting.
