It appears that we're headed toward a future where the SEC & B1G break away with a few additional schools to form a new top tier for CFB. I think that all the teams that are included in that transition will be very excited about CFB, at least in the near to medium term future. For those 40-50 teams, while every team won't really be an NC contender, being in the highest tier will be enough to maintain high interest and momentum.
I think for the G5 programs, where competing for the NC was never consistently (or even occasionally) realistic, that not a lot will change. Football at those schools have often been about conference championships and rivalries and getting back to campus to cheer for your team. It's possible that the popularity of CFB at those schools fall off, but the way that football is perceived at those schools doesn't have to change.
I think the biggest unknown is what is going to happen to the former P5 schools who don't make it into the new SEC/B1G top tier and end up being the new 2nd tier of CFB. A lot of those schools, while not NC contenders on anything like a consistent basis, at least (A) had a reasonable path to being an NC contender if the stars lined up for a year or two and (B) got to play legit NC contenders within conference on an annual basis. If that goes away based on the potential breakaway of the SEC/B1G + a few other schools, I'm not sure how the fans of those schools respond to this change. Do they accept that winning whatever national-level championship is available plus a conference championship is worthwhile and stay engaged in CFB? Or do they see themselves as the victims of all the realignment which has and will occur and simply check out of CFB based on no longer being in the highest tier? I have no idea what fans of these schools left behind by the potential breakaway of the SEC/B1G/other teams do when they are no longer in the top tier of CFB.