so the top tier teams in the SEC/B1G need a roughly equal number of middle of the pack/low tier teams.

I agree with you that I don't think they're going to expand to 24 teams. That's nuts because every time they expand, the additions have to add value at or above the current per-team revenue for the conference. There are very few teams that are worth $100 million per year as additions.

But I don't think you see new super-elite 8 or 10 team conferences formed because every conference game has a loser. You cannibalize your top teams too much if there aren't any lower tier teams.