The Mountain West conference proposed a 16-team playoff to the other conference commissioners last September, which will most likely get discussed this April, when the BCS has its annual meeting.
Personally, I like the idea of going straight to a proper 16-team playoff if the poobahs in charge ever decide to get rid of the BCS. If you're going to bit the bullet and create a playoff, you might as well get it right from the start. Four- and 8-team models aren't inclusive enough to get full buy in.
The nice thing about MWC commissioner Craig Thompson's plan is that it is big enough to include all 11 conference champions. Wait -- ten conference champions after his league merges with Conference USA. However, his plan then makes the mistake of failing to include all of the conference champions. Instead, his plan requires conference champions to be in the top 30 of some committee vote. This committee is the selection committee. Its 1-30 ranking would be used to select and seed the tournament.
That's too much work, plus it's politically expedient to include all the conference champs. The basketball committee model is much better. Just give the committee the ten conference winners, let them select the six at-large teams and seed the bracket. Easy peasy.
His proposal also has a limit of a maximum of three teams per conference, which is probably unnecessary. The odds of one league having three of the best six at-large teams are pretty small.
Another place his plan fails is trying to mix bowls and playoffs. Bowls aren't playoffs and not meant to be part of them. Bowls are week-long, chamber of commerce fueled events. They're vacations. Playoffs are business trips. Thompson wants the four BCS bowls to host quarterfinals. That is after the first round is played at campus sites, and before the semifinals are played at campus sites. There is no need for a neutral site round in the middle of the tournament. Just do it like every other level of football and play the whole thing at campus sites until the final.
The powers that be aren't ready for something like this yet anyway, and may not be for some time. However, if they ever do go to a 16-team playoff, include everyone, skip the bowls, and just play it.