If you replaced some of the OOC schedule at the start of the season with a group stage played at teams' home stadiums, you could have an 8-team playoff in which every team in the nation controlled their own destiny in reaching that playoff, without significantly lengthening the season, and it makes the regular season so much more interesting and important.
Here's how you do it: all conferences get 8 games to decide their pecking order, however they choose. Teams can also schedule 1 OOC rivalry game if they like to preserve traditional rivalries. If a conference does 7 games plus a CCG, they would be allowed 2 OOC games. Each conference is allotted a minimum of 1 spot in the 40-team group stage, with the ability to earn more based top-to-bottom conference performance in the group stages of past years. The conference determines the rankings of their own teams based on W-L records and whatever other tie-breaking criteria they choose, and then if the conference has N spots, the top N teams go into that playoff group stage.
The playoff group stage is 8 groups of 5 teams, and consists of 2 home games, 2 away games, and 1 bye for each team. Teams are seeded into their groups based on W-L records, and the top seed picks who they want at home and when they get their bye first, followed by the second seed, etc. You get a point for winning, nothing for losing, and whoever gets the most points in each group advances to the playoff. The other 32 teams would be bowl bound.
There would also be a bowl group stage, and a consolation group stage, consisting of the middle tier and bottom tier of teams, played in a similar way as the playoff group stage. This ensures everyone gets the home games they needs, and that they get to play at least a couple of games against similar talent each season. Group winners (and some runners up) in the bowl group stage would go on to play in bowl games against losers of the playoff group stage. The consolation group stage would not be bowl eligible, but they are playing to win more playoff group stage spots for the conference, so it still matters a lot.
This format ensures everyone plays 12 games, and you'd only have to play 15 games to win the playoff, which is what teams in a conference with a CCG would have to do now anyway. Win all your games, you are the national champion, guaranteed.
The number of spots a conference gets in the playoff group is determined by some metric of overall conference strength based on all group-stage games. I haven't worked out what that looks like mathematically, but basically if, on average, your teams are outperforming their seeding, you would take spots from conferences that underperform. Eventually, you would expect the outperform/underperform numbers to be pretty close to even once the correct number of spots was reached. The nice thing is that if it's wrong, it would self-correct fairly quickly.