I didn't go to law school, but it seems Liberty could sue and win. The NCAA rules are keeping Liberty at the FCS level because it's on a conference to invite them. They have good facilities, the desire, a decent budget... the things that would get any other school invited to FBS. What more can they do?

If Liberty has no path to FBS, then they are being unfairly discriminated against IMO.

With that said, let's say they win a suit and can upgrade as an independent. That's an impossible road for almost anyone, and Liberty would have a hard time getting home games. I doubt it's worthwhile to go FBS in that scenario.