8 is stupid. If you take the 5 conference champs, plus give 3 at large teams, you are making the conference championship a "play in game". You are basically giving the 3 at large teams a bye.
Look you are not going to get 16, won't happen. No matter how much money is involved, they are still college students and there is no way college presidents buy off on extending the season. Also as I mentioned above, 16 favors the blue bloods able to go three deep.
8 is better than 4, yup you might get three teams that did not play 13 games........more probable is you will get a couple conference championship losers. I could make a pretty good case for Ohio State getting in to an 8 team play-off before Iowa this past year. I would think playing a Notre Dame type schedule and not playing 13 games is more impressive than losing a championship game having played 4 or 5 cupcakes to start the year.