Let's spitball a few more ideas...
I would keep the 12 team college football playoff out of the bowl system entirely, with first and second round games on campus the two weekends before Christmas and then both the semifinals in an NFL venue back to back on the first weekend of January with the championship game in the same location the next weekend. Media could bid on the on-campus games or the 3 neutral site games, but not be rewarded both. Spread that stuff around a little.
Immediately after the playoff announcements, institute a bowl game draft outside of conference tie-ins, with selection order determined by payout. Half of the payout for these games would be equally distributed to the players, with 2/3 going to the winning players and 1/3 to the other team players. (Our game this year would have earned winning teams' players about $15K each. A sugar bowl wining team would earn $56K.) In order to be eligible, you need to be on scholarship or have assigned walk-on status by your coaching staff. This will ultimately eliminate all games that exist only to fill an ESPN TV slot. These games would be played around the playoff games between December 19 and January 1.
Transfer portal can open December 1, but will close December 15, or the last day of fall semester, whichever is later. Rip the band-aid off and get it over with, rather than make it a weeks long thing. All players who elect to transfer will be disqualified from playing in any bowl games or receiving game participation checks. Once you enter the portal, you are no longer considered part of your team.
Player opt outs from bowl games are a personal business decision and should be allowed but players who declare will not be considered eligible for game bonus, since they have also left the team. If the coaches choose not to use the player, that is between them. I don't see a way around that.
The Monday before Christmas would be the first signing day for the following season out of high school. Still allows early enrollees to get onto campus for spring semester, and coaches to make decisions knowing the final status of the roster after the portal closes. This signing window would still close on the first day of class.
This compresses the player schedule a bunch, but I honestly believes it's in the interest of all parties to go that way, even though it is a busy time for coaching staffs.