Thats where we would disagree. CFB will never be popular enough to have its national audience depend on 32-40 teams or even 48 for that matter. Your telling too many fan bases they don't matter.
I have watched college football my whole life because the state I live in has two teams to watch not because of the value of the product in comparison to the NFL. As I have aged I have realized what a crap show CFB ends its season on and their desire to engineer matchups and outcomes. At times, I almost feel like I am watching WWE instead of football, due to all of the engineering. So I have watched more NFL especially at the end of the season because CFB has no purposeful ending.
But after watching about 5 NFL games yesterday it just reinforces it is football on the highest level and if you don't give a CFB fan a reason to watch due to a team involved in the product its inferior to the NFL. It will be like making CFB AAA baseball and nobody real cares about AAA baseball. Then when you have 32-48 teams playing themselves and you have schools having a lot more losses than they previously had, it will be a challenge to get those schools fans to stay involved at the numbers they wanted. Especially, the casual fan.
Similar starting point, different conclusion. The SEC and ESPN have already figured out it is regional/not national- so why pay for a national map with redundancy? Most of those excluded by nature don't have many fans that add TV revenue to the current average of the P48, if they did, they'd be invited.
Will it go down? Yes, but not as much as what they just avoided paying for. That is the key. That is inherent to the exclusion. The elasticity will only improve after slowly suffocating the fans over 10-15 years.
Think of it this way. If the SEC makes a network enough to justify on average paying a team $80 million, why pay Big 12 teams $30 million to get a fraction of them to watch the SEC? Make the Big 12 fans not care at all, thereby paying them nothing. Maybe that means you only get $75 million worth of viewership revenue per SEC team, but you just saved $30 million by no longer needing to pay the Big 12 schools.
I assure you the networks have done that math. They've studied the elasticity of exclusion, and they'll make more.
I also think you're overestimating losing the non P48 schools in terms of losing the ability to be more national and less regional. Adding the North-South polarization makes people pick sides. It will be bigger than now, but with less teams.
NLI is a bigger threat to their product imo. Losing Big 12 fans that don't watch at the level of the P48 is good math, although cold hearted. Losing the BIG and SEC fans of the P32-P48 because they don't want to watch kids making millions of NLI may be a bigger deal