There are simply not good enough teams out there that will produce enough revenue for the Big 10 / SEC to hit 24 teams. You simply don't have the schools available that are going to add that kind of value. Also, the Big 10 and SEC are working together *Individually* to maximize their revenue and power, they are not working together to form a 2 conference super-league.

Look at the teams that actually add value (in no particular order):
1. Notre Dame - available but picky
2. Washington/Oregon - Add way more than Rutgers, but less than Ohio St., Michigan, LA schools, Penn St.
3. Clemson, Florida St, Miami - locked up by grant-of-rights until sometime in the 2030s, but could help the SEC.

Is there any teams I missed? I have a hard time seeing any other schools out there that really move the revenue needle.

I think the next round, likely when the ACC drops it's grant-of-rights, is for consolidation. Ohio State may figure out it doesn't need Rutgers, and Alabama may figure out it doesn't need Vandy (despite their good baseball). They get together and form 2-3 new conferences of 10 or 8 elite teams, and maximize their money and power even more. Since any conference can now have a championship, it makes small, elite conferences more profitable. It is about money and the playoffs, not the bowl games and secondary teams.

With second level P5 teams, large conferences make sense because you can "monopolize" their content into a single TV package to maximize revenue. But at the top level, large conglomerations stop making sense because it is only the very elites that are driving the revenue and playoffs, and good schools are merely filler that can't move the revenue needle.