I think a college football playoff is a bad idea. It's a bad idea for many reasons, but I'd like to look at perhaps the most obvious.
How many teams do you invite?
Much of the chatter in favor of a playoff is that it would be more "fair". I disagree. If we look at the historical numbers we can see why this is.
Every year, there are some teams that indisputably be included in a playoff: the major conference undefeateds. This year, Ohio State is the only such team.
Every year there is also a second tier, teams that if we invite one of them, we must invite all of them. This year, there are two such teams: Florida and Michigan.
The problem is that the number of teams in these categories fluctuates every year. Looking at the last ten years, here's a chart showing how the number of deserving teams varies:
There was some subjectivity in deciding the second tier teams, but not much. (Handy data is available at http://www.soonerstats.com/fb/polls/index.cfm and http://www.jhowell.net/cf/scores/byName.htm.)
So how many teams do you invite? If you have one game, you've got a great matchup in 2005, 2002, 1999, and 1997. The other six years, a one game championship game would be unfair. And so on, for different numbers of games.
If you want more than one game, we always end up with between three and six deserving teams. It's just not possible to create a fair system.
Fortunately, the world keeps turning just fine without a fair college football system. In fact, one could argue that the sport does quite well. There are no shortage of fans. There's certainly no shortage of money! What's the problem with the system we have now?