One thing that will probably happen long before the playoff expands:
Evening out the schedule. Someone will get left out. Maybe it is a two loss PAC-12 team. Maybe it is the #2 SEC team.
If the SEC gets left out, they go to 9 conference games.
If the PAC-12 gets left out, they go to 8 conference games.
I really don't think the Big 12 is the big lynch pin like BYU fans hope. My reason? They play 9 conference games. The ACC, Big 10 (though not for long) and SEC plays 8. Right now, a one loss PAC-12 or Big 12 gets in over a one loss ACC/SEC/Big10 team (if SOS is true) because they play more P5 teams. So, with the Big 12 playing more conference games, they don't need the championship game for SOS reasons. They have that "extra" game built into their schedule already.
Let's say Stanford ends up with two losses but wins the PAC-12 championship. I think they get in over a one loss Ol' Miss team that didn't win the SEC title game because of their schedules.
Look at Ol' Miss's OOC games:
Boise St
Louisiana
Memphis
Presbyterian
vs
UC Davis
Army
Notre Dame
additional PAC-12 game
PAC-12 title game
Stanford's schedule is much, much tougher.
Same with Miss St.
Their 4 OOC? Southern Miss, UAB, South Alabama, UT Martin.
The committee will have to decide what is more important. If SOS is, then the SEC will get killed in the playoff selection. If that happens, they will move to 9 conference games. If the SEC does not get killed, and a two loss PAC-12 gets snubbed for a one loss SEC then the PAC-12 will move to 8 conference games.
Anyways, my discourse is done.
tl/dr version:
I think conference games all go to 8 games or all conferences go to 9 games before the playoff is expanded.