You are right that one can end up "footballed out."
I bet that probably has helped kill all the other spring football leagues.
It has to have impact, being played "out of traditional season." Kind of a tough spot because in addition to less star power, only football diehards are likely to stay engaged with the game once spring rolls around. But if it's pushed closer to regular time of year, it would have no way to compete w/ NFL (USFL tried to switch to fall schedule and that pretty much finished it off, IIRC).