One idea that crossed my mind was to have 5 regional championship games instead of the traditional conference championship games.

This is how to get P5 teams to buy in. Each P5 conference would be a sponsor of 1 regional championship game. The P5 sponsor gets to keep all revenue from the game. The 2 teams that make the RCG would be the 2 highest ranked teams in that region. The region's would be defined this way

North Region
Sponsor: Big Ten
Teams: All Big Ten teams, All MAC teams

East Region
Sponsor: ACC
Teams: All ACC teams, All CUSA teams, Notre Dame, Army, UMass

South Region
Sponsor: SEC
Teams: All SEC teams, All Sunbelt teams, Liberty

Central Region
Sponsor: Big 12
Teams: All Big 12 teams, All AAC teams

West Region
Sponsor: PAC
Teams: All PAC teams, All MWC teams, BYU, NMSU

Now if you wanted to shrink this to 4 regions instead of 5, it gets a little trickier, but would probably have to be split this way

North Region
Sponsor: Big Ten
Teams: All Big Ten teams, All MAC teams

East Region
Sponsor: ACC
Teams: All ACC teams, All AAC teams, All CUSA teams, Notre Dame, Army, UMass

South Region
Sponsor: SEC
Teams: All SEC teams, All Sunbelt teams, Liberty

West Region
CO-Sponsor: PAC/Big 12
Teams: All PAC teams, All Big 12 teams, All MWC teams, BYU, NMSU

It works better if this change is made in conjunction with adding one additional playoff week. Then you have a field of 16 with each P5 division champ (10), top G5 division champ (1), and 5 at large bids.

Just say no.

I'm sure the conferences are going to be willing to risk the revenue level of what is currently assured to be a desirable game for sponsors for what most assuredly would not.