I think that the major legitimate obstacle is the need to schedule venues well in advance.
I don't think that anyone should or even could use this year as a reason to push for 8 teams. Does anyone think that 3-loss Auburn, #7 in the CFP rankings, should be playing for a national championship?
Sure. I can see that as a legitimate obstacle. However, I also see it as another modern day malady of the tail wagging the dog.
A hundred years ago if two teams wanted to play, they got out on the field and played. Selling tickets to spectators was beside the point.
Nowadays, we're so worried about everybody getting their dollar that we're actually questioning whether or not a game should be played if it creates a hardship for a venue?!!!
Craziness!
Most schools don't know which bowl they're going to play in until the season is over any way.
Schools that love baseball clamor to host regionals and super-regionals. They submit bids to the NCAA who pick and choose. Not all get picked. There are no guarantees.
March Madness works the same way.
Here's what you do. You let everybody know that there may or may not be a half dozen or more games that need to be played in late December or early January and you encourage them to bid.
Clemson and Alabama have been to the last three CFPs. You think they wouldn't bid? Other teams with nice facilities and high ambitions might bid. Think Jerry Jones would let the opportunity pass?
Before the season starts the NCAA could name the 10 finalists or whatever and as the playoff scenario shakes out the necessary sites will be chosen.
What's the worst that could happen? Some stadium sets empty one Saturday because they took a chance on hosting a playoff game and it didn't pay off?
Are we going to let some butthurt millionaire, franchise or university prevent us from embracing a sensible playoff system?