Infinite. There is no 'good enough' amount of NIL; as the rules are, more is always better. If a school comes up with $1B then some other school will want $1.5B.
Problem is it's still the wild west. Honestly I think the NCAA should set some revenue sharing cap above the $20.5m limit--maybe, 30? And then put something in place to regulate NIL such that it's only legitimately NIL. I mean, what happens if the IRS decides that Bob Valley Chevrolet's $4M expense to pay the Bob State QB wasn't *really* for those five tweets to his 600 followers? They reboot the whole system *again*?