First, this will likely happen before 2026, second this is likely to dampen much realignment for a while.
A 12 team playoff with 6 bids going to the 6 highest ranked conference champions basically means the P5 conferences all get an auto bid as well as the top ranked G5 school. 6 at large teams basically means ND is guaranteed a bid with a Top 12 finish.
I think this will be more than fine for ND and they will stay independent and get a new deal from NBC so they play on NBC in the afternoon and B10 players a night game on NBC.
For conferences, it makes it less likely they want to poach teams from other conferences. Why go to another conference (B10 or SEC) where your odds of ever getting a playoff bid is almost nil when you can stay where you are and you just have to beat teams that are more in line with you. Why would you add teams unless they are additive to your media deals?
If you're say Oregon, would you rather be in the B10 and getting more money but competing against Ohio St, Michigan, WI, Mi St, Penn St for an auto bid or stay in the PAC10 and have to compete against WA, Stanford, Utah for an auto bid. If your Clemson do you want to go to the SEC and compete against UGA, AL, TX, OK, TX A&M, FL for an auto bid or in the ACC?
The deal also means the B10 and SEC are likely to have multiple playoff teams every year.