There are 12 playoff spots.
Six of those go to the highest ranked conference champions. (ACC/Big 12/B1G/PAC/SEC/G5).
The other six bids are for at large teams (Notre Dame and others).
The odds of securing a automatic playoff bid for the PAC is (1/10) and Big 12 (1/12).
With expansion, the conferences can secure "de facto" autobids in the at-large portion. The SEC and B1G are almost assuredly going to get at least one more team in through the at-large section, maybe more.
The expanded Big 12 could secure a "de facto" auto bid in the "at-large" group. Meaning the Big 12 could receive two bids for 16 teams. Accordingly, your odds of making the playoffs are (1/8) rather than (1/10).
If the CFP award process changes, then those odds likely become more fixed or more favorable for an expanded Big 12.