I loved the original USFL. Was it on par with the NFL? No, but it did feature the fun of "Bandit Ball" and Steve Spurrier down in Tampa Bay, a pretty solid Philadelphia Stars team, and Bobby Hebert (among others like Sam Mills, Ray Bentley, Kent Hull, etc.) the chance to learn and grow into a pretty good NFL QB - an opportunity that I doubt he'd have had without the upstart league.
I think a feeder concept, like NFL Europe was, would benefit the NFL. How many players get drafted into a system that doesn't really fit their talents? How many get drafted only to find that GM/Coach fired soon after and a new regime installed that wants to clean house? How many simply need coaching and playing time to become viable players with a chance to make an NFL? How many would love the chance to get paid to play football while trying to chase their dream?
America has an insatiable appetite for football. If put together well, with innovations tried out in this league and quality teaching and coaching employed with a tie to the NFL, I think it can work. I'll be watching ... hope they bring the Oakland Invaders back. Sweet uniforms!