If the SEC goes to 16 teams, I think it's only a matter of time until the rest of the power conferences do too, or at least attempt to.
The Pac-12 has made it clear they will not add religious institutions. In other words, good bye BYU, TCU and Baylor. Idk if Texas Tech's academics are too bad for the Pac-12 and the likes of Stanford and Cal-Berkeley, but if the Pac-12 wants to get to 16 teams without adding the likes of Boise State and BYU, the only way I see that happening is if they extend an offer to Texas Tech, Oklahoma State, Kansas State and Iowa State. I'm not sure who else they could honestly grab unless they wanna promote someone from the Mountain West. I think their options would be to either try to snag those 4 Big 12 teams or stay at 12.
The Big Ten would need 2 more teams to reach 16 teams. Now, the Big Ten has already shown they're willing to be odd man out and sit at a weird number for decades when they added Penn State in 1990 and then stayed at 11 teams until they added Nebraska as their 12th school in 2011. It doesn't look like the Big Ten is willing to accept institutions that aren't AAU members. If you look at the list of schools currently in a P5 conference that are also AAU members (I'm excluding any SEC members and Texas), the list includes:
Washington, Oregon, Cal, Stanford, USC, UCLA, Arizona, Utah, Colorado, Kansas, Iowa State, Pitt, Virginia, Duke, North Carolina, Georgia Tech.
So you have a bunch of Pac-12 schools that are super separated geographically, two Big 12 schools and then several ACC schools. The ACC institutions signed away their Grant of Rights through the 2035-36 academic year and additionally would have to pay a $50 million exit fee if they chose to leave the ACC before then. Additionally, Notre Dame is contractually obligated to join the ACC if they join a conference before then as well. The way I see it, the Big Ten could decide to either stay at 14 teams until 2 teams free up from the ACC they'd want and then pick them off. They could add one Big 12 team (would probably be Kansas) and then sit at 15 teams for the next 15 years before picking off an ACC team for their 16 member, or they could add both Kansas and Iowa State.
The only way I see the ACC getting to 16 teams is if they finally were able to force Notre Dame's hand and then add one more team, whether from the American or left over Big 12. Or they could just go ahead and add 2 teams that are in the American or left over Big 12 right away.