I had been a proponent of a playoff system for many years, going back to the 1980s. But the mechanics of this is difficult. How is this any different than the current BCS format, other than adding two more teams and one more game?
If you take 4 teams, team No. 5 will always feel slighted. If you take 8 teams, team No. 9 will complain. If you take 16 teams, it will be team No. 17. And so. The basketball tournament is up to, what, 68 teams and every year you hear whining from some team with 12 losses claiming it got jobbed. (Truth be told, there are probably too MANY teams getting in, not too few.) So I can't see how a 4-team playoff is going to help much.
How would you justify excluding a major conference champion while taking more than one team from another conference?