Why is everyone so worried about an 8-4 USC type of team getting into the playoff? In an 8-team playoff, they'd still need to beat 3 other playoff teams to win it all. In a 12-team playoff, they'd have to beat 4 because I'm assuming they'd be a low seed.
And if they did that, they would have earned it.
Realistically, how does a team get to 8-4, that could still win the playoff? Almost invariably it would be something like a rash of injuries early in the season, that healed up over time, and once they got to full strength, they ended up being pretty bad-ass. Sounds like a worthy CFP champion to me. *shrug*