Notre Dame, Oregon, Washington, Clemson, and Florida St would all make sense to add for those conferences. After that I agree it gets more questionable. My guess is if they both went to 20 then Stanford would be included for Big Ten and Miami and Virginia Tech would probably be next 2 on the list for SEC. You could argue maybe Oklahome State or even NC State instead of one of those other ACC schools, but the only reason to add one of them would be to get to an even 20 instead of stopping at 19.