Make it the four, top-rated CONFERNCE champs...with semis played at home. Then your confernce championship games mean one helluva lot more than they do now, and should draw much better TV ratings than before. As this means more ESPN money for all these broadcasts, it might stand a chance. As this also means Big-10 teams have a better chance at the NC game, Big JIm Delaney (a.k.a. , The Prince of Darkness) ought to endorse it, so it would have even a better chance. SEC would fuss, but they should always be ranked higher than their frozen northen conterparts anyway, so...is this REALLY a problem?
You want to open up the playoff to 8 teams, then go ahead ... top rated teams can sub in for conference champs up and down the line, as many posters here have said. If it's only four teams, then you keep the BCS-type, style points to a minimum. The two other problems then (with eight teams and keeping the home-team advantage) are: 1.) doubling the travel costs to root your ultimate national champ home, and 2.) adding another week to the season, which in this collision sport may place too high a premium in staying injury free.
So, al-in-all, I can embrace the positives that the more restrictive four-team-formula brings with it, but ONLY if you also minimize the style points and beauty contest element in picking the final four. That, my friends, clearly argues for the conference-champs-only criteria.