The NCAA's power is solely, and wholely, granted to it by its member institutions.
To date, those member institutions have fallen in line with the NCAA on any types of payments to players, for a multitude of reasons, some of which are wholesome and some of which are less so. Regardless, as long as those member institutions toed the line, then the power remained with the NCAA.
But even aside from the state legislatures and their activities, there is now more sentiment than I've ever seen before, coming from coaches and athletic administrators all over the country including some of the richest, most powerful, and most prestigious, universities, that some type of payment should be allowed. And allowing 3rd party endorsements like this is the safest* way for universities to attempt to handle this.
*safest in this sense only because it has no direct risk or liability for the university since they wouldn't be providing any of the payments
I think the tide is changing on this issue, and I think we're talking WHEN not IF this occurs nation-wide. The only question remaining is, will the NCAA be a part of it, or will the member institutions revoke the power they've currently granted the NCAA, and move it elsewhere, into a separate governing body?