An NFL "D" league would be sweet. My ideas:
Scrap NFL Thursday night series. Play the developmental league games on Thursday on NFL network.
16 teams, each co-owned by teams in opposite conferences who are somewhat close to each other. SF and Oakland. Miami and Tampa. Dallas and Houston. That kinda deal.
Two conferences. Ten game season. Four teams make the playoffs. After NFL week twelve, rosters expand to 60 and they can pull a few guys up.