A player controlled league could happen, and it would start by the players retiring. Just like a team can cut a player at any time, a player can leave at any time by retiring. It would also take the millionaire superstar players to invest in the league, and risk alienating fans with 32 new teams.
With the state of things, how hard pressed would fans be to make the jump to the new league? The NFL and the PFL (PlayersFL) would fight over college players, and if the PFL won over incoming rookies where would that leave the NFL? Sure for the first seasons the PFL would have to rent college stadiums, and arenas but it would boil down to do you want to see good football, or do you want to see the D league Pittsburg Steelers? There are a lot of football players out there in the European NFL, arena football and the CFL, but the reason there in those leagues is because they can't make the NFL, and for me it's the level of competition that makes it exciting. College football is a little more exciting live (imho) than the NFL, but the excitement comes from the students who have no disillusions about being part of the team, and that doesn't translate to T.V. I garuntee you that ESPN would show PFL games, they show arena, and the other two leagues when they do something spectacular, and a PFL would have tons of highlights.
Of course, this is just a pipe dream, but it could work. It would maybe need some outside investors to get started and who would become the 'league' setting rules, validating contracts, dividing revenue, and taking some for themselves as well, but maybe there are enough crazy billionaires like Mark Cuban to do something like that. If I was Mark Cuban I would be calling every other billionaire that's ever tried to own an NFL team, and offer the NFL players a new league with revenue sharing on a slightly higher scale than what the NFL has, in that it would include the players.
And I disagree with a salary cap. Players should get the money they earn the team because the team wouldn't earn it without them.