The only way that an alternative/secondary football league is financially viable is if it can acquire and retain national advertising sponsors. The chances of that happening independent of the NFL are very low, and the chances pretty much vanish with McMahon running the show. I don't see how it even gets off the ground.
I would, however, like to see a "minor league" developed and backed by the NFL. As
@convertedpatsfan suggested, perhaps running from mid-February through mid-April (six to eight weeks).
Maybe six teams, perhaps all located in the Southeast to reduce travel expenses. No playoffs. More like baseball Spring Training than a real "league". Keep it real simple and real inexpensive. Broadcast on the NFL Network to make it easier to rope in a few existing national sponsors, but maybe sell some rights to ESPN or Fox (and overseas broadcasters) for "co-broadcasts". The CFL might even cooperate in it.
Same playing rules as the NFL game, but (obviously) a lot more roster flexibility and pre-set salaries for all players, regardless of position or experience - probably PS level or a bit less.