Depends on what the Big 10, ACC and PAC-12 champions look like. What if there's an undefeated team coming out of Big12? Then, what if a 2 loss #12-15 ranked Tennessee or Florida team somehow beats a #1, undefeated Alabama team?
I think the idea that the SEC champion gets in "no matter what" just isn't true.
It should be. In fact the winner of each Power 5 conference should get in plus one wild card team.
Seed the top 2 with byes. The other 3 plus wildcard plays first round - winners advance to face the top 2 etc