I think this makes a lot of sense for the NFL but if they really want it they are probably going to have to help fund it. Otherwise, it is unlikely to succeed.
I agree. There was a pretty large semi-pro league
on the east coast when I was a kid. I remember my dad taking me to a couple of games. They were pretty entertaining. The league had the support of the NFL for several years, but at some point the NFL pulled out and the league collapsed a couple of years later. I don't recall why the NFL pulled out. Perhaps they didn't feel they were getting sufficient bang for the buck.
Plus, football wasn't anywhere near
as over-exposed as it is today with a bazillion games on TV every weekend. So seeing a live semi-pro game was more of an attraction than it would be today.