A 13-0, 12th-ranked team from the MAC is very similar to a 13-0, 10th-ranked team from the American East. UCF beat #7 Auburn by a TD in a New Year's Six bowl game while WM lost to #8 Wisconsin by a TD in a NYS bowl game. I don't think WM was any less deserving of consideration than UCF was and is.
A six-team playoff is silly regardless since it requires an extra week of games and there'd by no reason to cap the playoff at six rather than eight. But I think an undefeated champion from a non-Power 5 conference that meets a certain ranking threshold (that's not necessarily eighth or better) automatically getting a spot in an eight-team playoff would be a good thing.