The move to bigger conferences is the attempt to create more compelling games. Theory is even a oklahoma vs vandy is more interesting than ok vs wv. etc. They pimp up how good all the top 6-8 teams in big10 and sec are to drive viewership.
and the post season, well, can it generate enough revenue to justify diluting the quality of play? Let's be honest, there just aren't enough great players to go around for a the best sunbelt team to compete well against the top 25-30 teams in the nation.
I think the concept you present makes it sort of more interesting for the fans, but that first weekend of 16 games will have a 13 boring games.
Maybe cut it to 16 teams. 5 conferences with 2 auto bids and 6 at large.