I don't think we'll ever see things get beyond a Final Four. Absolutely no one who makes these decisions favors expanding to 8 or 16 teams.
In 1991, do you think anyone really imagined a 4 team playoff? If they go towards a 4 team playoff you are right in that it will likely end up with just the top four (but they'll probably sneak in a no 3 from one conference rule). But, once the major conferences start to see they are regularly left out, the pressure (which already exists in great deal, I've seen and heard many people here, on ESPN, etc... state their ultimate goal is 8 or more) to expand further will set in. It happened to the MLB, NCAA, NFL, etc... it
will happen to college football if this line is crossed.
You can't unring this bell. If there's a playoff, college football will no longer be different from the other major sports. And, ultimately it will place the things that make it so different (generally crowning the best team champion, bowls, polls, etc...) on the path to extinction. I've heard so many times about how everyone else has a playoff. Well, guess what? Everyone else has a system that includes conference/division champs. If you think the two can remain apart forever you're being quite unrealistic.
The only way to prevent this from happening ultimately, is for more people to put their foot down and say, I want to preserve the bowl games, I want the regular season to matter, and I want the most worthy teams to play for a championship. What can't happen, is this kneejerk support for a playoff and this manipulated anti-BCS lunacy the AP is spreading (which gives a rubber stamp to the NCAA basketball playoffs) be allowed to prevail. I'm not completely anti-plus one. I just know what it will really become, and what people really intend for it to be. It's for the sake of inclusion, not excellence and in practice it will not do a better job of crowning a deserving champion. All it will do, is put us one small step away from destroying what's best about college football.
The ultimate goal for many, is to make it less about excellence and more about inclusion. Study over what has happened to all the other playoffs and show me where I'm wrong. It's ultimately an ideal, a belief system which says more should have a chance and that being great shouldn't mean so much.