I think most people's problems with that can be summed up like this:
1) There aren't 12 AQ conferences, unless you changed the rules that make a conference an AQ conference. Realistically speaking, this won't happen.
2) Given reason number one, you'd either have to just let every conference winner into the playoff (which won't happen) or you'd have to give out several wildcard slots. The reason all conferences won't get a playoff berth automatically is because the parity between college football conferences (between AQ and non-AQ) is significantly different than the divisions in the NFL, for example.
As far as wildcards go, the more teams you position into the playoffs the more watered-down the regular season becomes, which is what no honest college football fan wants to have happen. Despite it's problems, the CFB regular season is what makes CFB so unique and great. A water-down regular season is inevitable with a playoff, however.
I think most college football fans would be against a 16-team playoff, mainly because every conference will not receive an automatic berth, which means you'd need wildcards. And as I said, too many wildcards waters it down too much in my opinion.
1) There are 12 conferences IIRC--if there's only 11 now, then that's fine, as that now leaves five wildcard slots. If we're doing a playoff, it will have to include all conferences, unfortunately, or Washington will get involved.
2) See #1, specifically the Washington part.
3) Wildcards won't "water down the season"--if anything, it would reward many deserving second-place teams in conferences based off of seasonal play. The only possible thing a wildcard would water down is the conference title game...and frankly, if that means the difference between a 1-seed layup game for the first round or having to go on the road to play a competent team and possibly get knocked out early, that will likely be more than enough motivation.
Again--I'm not getting into the debate of whether or not we should have a playoff. Just saying if we have one, I think this is the way to go, as it rewards seasonal play (especially for great teams that don't win their conference), no conference is left out in the cold (yes, even the MAC or Sun Belt, unfortunately), we keep the secondary and tertiary (toiletry?) bowls, and use existing tools (BCS poll).
The only way this would happen is if it's a win-win for everyone. Again--not saying it's right or wrong, just trying to be practical about how it would be implemented if it comes to pass.