I think most of the opposition to it here is more we just don't have this organic collection of hundreds of clubs that could be meaningfully organized into a workable system. Soccer is probably the closest, but the lower tier leagues have a lot of ways to go to make it a reasonable proposition. I think the other leagues that have minor league systems are just too entrenched in their system to be able to adapt. The other issue is how the NCAA fits in.
While the parallels to our closed leagues are obvious, it still feels like this is more akin to the NHL 06 teams trying to splinter into their own league, or an NFL Super League with just the Cowboys, Giants, Patriots, Packers, Steelers, Raiders, Eagles, and Bears, etc...