Here's an example of how a 12-school playoff would have worked out since 2014, with liberties taken for recent realignment. IOW, the conference totals are skewered because I'm including Oklahoma as part of the SEC; USC as part of the B1G; Cincinnati, UCF, and Houston as part of the B12; and ND needing to finish in the Top 10-12 (also consider that ND never gets a bye since ND is not part of a conference).
Looking at these playoff schools over the years, the 12-school playoff will prove to be wildly popular, and, to avoid byes (and generate more $), I foresee a 16-school playoff in short order. Because of gameday attendance, I suspect the idea of "keeping the bowls alive" will be soon scraped in favor of more $ by playing at the home of the higher ranked school. Emulating the NFL, and, again, assuming attendance holds up, the finals will be played at a predetermined site as a college version "Super Bowl", along with all of the associated hype.
The following from CBS (with notations for realignment "what ifs"):
2021
Byes (Top Ranked Conference Champions)
1) Alabama
2) Michigan
3) Cincinnati (B12 conference champion)
4) Baylor (BU falls to RoF since not a conference champion)
Rest of Field (X=Conference Champions)
5) Georgia
6) Notre Dame
7) Ohio State
8) Ole Miss
9) Oklahoma State
10) Michigan State (MSU drops out due to need for next up conference champion)
11) Utah = X (Utah rises to 4 as PAC conference champion)
12) Pittsburg = X
SEC = 3
B1G = 2 (3 - 1)
ACC = 1
B12 = 3
PAC = 1
Others = 1 (0 + 1)
ND = 1 (Top 10-12)
2020
Byes (Top Ranked Conference Champions)
1) Alabama
2) Clemson
3) Ohio State
4) Oklahoma (SEC: OU falls to RoF since not a conference champion)
Rest of Field (X=Conference Champions)
5) Notre Dame
6) Texas A&M
7) Florida
8) Cincinnati = X (B12: Cincy rises to 4 as B12 conference champion)
9) Georgia
10) Iowa State
11) Indiana (IU drops out due to need for next up conference champion)
12) Coastal Carolina = X
SEC = 5
B1G = 1 (2 - 1)
ACC = 1
B12 = 2
PAC = 0
Others = 2 (1 + 1)
ND = 1 (Top 10-12)
2019
Byes (Top Ranked Conference Champions)
1) LSU
2) Ohio State
3) Clemson
4) Oklahoma (SEC: OU falls to RoF since not a conference champion)
Rest of Field (X=Conference Champions)
5) Georgia
6) Oregon = X (OR rises to 4 as PAC conference champion)
7) Baylor
8) Wisconsin
9) Florida
10) Penn State
11) Utah (Utah drops out due to need for next up conference champion)
12) Memphis = X
SEC = 4
B1G = 3
ACC = 1
B12 = 1
PAC = 1 (2 - 1)
Others = 2 (1 + 1)
2018
Byes (Top Ranked Conference Champions)
1) Alabama
2) Clemson
3) Oklahoma (SEC: OU falls to RoF since not a conference champion)
4) Ohio State
Rest of Field (X=Conference Champions)
5) Notre Dame
6) Georgia
7) Michigan
8) UCF = X (B12: UCF rises to 4 as B12 conference champion)
9) Washington = X
10) Florida
11) LSU
12) Penn State (PSU drops out due to need for next up conference champion)
SEC = 5
B1G = 2 (3 - 1)
ACC = 1
B12 = 1
PAC = 1
Others = 1 (0 + 1)
ND = 1 (Top 10-12)
2017
Byes (Top Ranked Conference Champions)
1) Clemson
2) Oklahoma (SEC conference champion)
3) Georgia (GA falls to RoF since not a conference champion)
4) Ohio State
Rest of Field (X=Conference Champions)
5) Alabama
6) Wisconsin
7) Auburn
8) USC = X (B1G: Not a conference champion)
9) Penn State
10) Miami (Miami drops out due to need for next up conference champion)
11) Washington (WA rises to 4 since WA wins the PAC with USC to B1G)
12) UCF = X (B12 conference champion)
SEC = 4
B1G = 4
ACC = 1 (2 - 1)
B12 = 1
PAC = 1
Others = 1 (0 + 1)
2016
Byes (Top Ranked Conference Champions)
1) Alabama
2) Clemson
3) Washington
4) Penn State
Rest of Field (X=Conference Champions)
5) Ohio State
6) Michigan
7) Oklahoma = X (SEC: Not a conference champion)
8) Wisconsin
9) USC (B1G)
10) Colorado
11) Florida State (FSU drops out due to need for next up conference champion)
12) Western Michigan = X
SEC = 2
B1G = 5
ACC = 1 (2 - 1)
B12 = 0
PAC = 2
Others = 2 (1 + 1)
2015
Byes (Top Ranked Conference Champions)
1) Clemson
2) Alabama
3) Michigan State
4) Oklahoma (SEC: OU falls to RoF since not a conference champion)
Rest of Field (X=Conference Champions)
5) Iowa
6) Stanford = X (Stanford rises to 4 as PAC conference champion)
7) Ohio State
8) Notre Dame
9) Florida State
10) North Carolina
11) TCU (TCU becomes B12 conference champion since OU is in SEC)
12) Houston = X (B12: TCU wins B12 so Houston drops out due to need for next up conference champion)
SEC = 2
B1G = 3
ACC = 3
B12 = 1 (2 - 1)
PAC = 1
Others = 1 (0 + 1)
ND = 1 (Top 10-12)
2014
Byes (Top Ranked Conference Champions)
1) Alabama
2) Oregon
3) Florida State
4) Ohio State
Rest of Field (X=Conference Champions)
5) Baylor = X
6) TCU
7) Mississippi State
8) Michigan State
9) Ole Miss
10) Arizona
11) Kansas State
12) Boise State = X
SEC = 3
B1G = 2
ACC = 1
B12 = 3
PAC = 2
Others = 1
