The only professional football league other than the NFL that has a chance to succeed is the one that goes head to head with college football with the best 18-24 year olds who don't go to college playing in it and trying to get drafted. No one wants to see 2nd rate talent playing meaningless games but if you put talented 18-24 year olds who decided to skip college, flunked out of college, or were ineligible on the field and could grow it to rival the college game, I think people would watch it. College baseball has never been a huge draw outside of college towns because everyone knows the best talent at that age is in the minor leagues. On the other hand, college football is a juggernaut because the best talent in the world at that age is on the field. Poach some of that talent and combine it with the talent that couldn't make it to college and maybe some 23-24 year olds that played in college but didn't get drafted and you could likely compete against college football or at least build a successful league who's main purpose is to develop NFL talent.