So we're really just debating over whether to stop at 6 teams vs 8 teams, otherwise we pretty much agree.
The big problem for the cfp right now is that the Group of 5, the PAC12, and the Big12 are unhappy. Between them they have a total of 4 appearances in cfp, 1 appearance in championship game, and zero titles. This compared to the SEC, ACC, & Big 10 which have 12 cfp appearances, 7 championship game appearances, and 4 titles. Now the truth is the SEC, ACC, & Big 10 are just playing better football, but that's not how the Group of 5, the PAC12, and the Big12 see it, and at some point, unless this trend changes, they are likely to demand an expansion of the cfp, so we may be debating a moot point. Now whether that takes 5 years or 15 years is anyone's guess, but it's probably coming.
As for #7 & #8, last year Auburn was #7 and I think it's fair to say that they were very capable of beating Alabama (who they had already beat) or Clemson (who they lost to by one score on the road without their best player).