I think if they get some known college names in that may not exactly be NFL quality, it could gain some popularity. Especially QBs like Jake Browning or Quenton Flowers who have talent but just won't ever get a chance at one of the 32 jobs in the NFL. Name recognization would be huge for the XFL.
I think this will be the natural progression if they can last 2-3 years. This is basically expansion rosters, but these guys that don't get drafted, or get cut from teams during the NFL season will be able to sign with them and showcase themselves between the NFL season ending and the draft. I imagine teams not making the playoffs will be regulars at these games.
The operations hangup I have, is will this league be ok being so transient player wise? You'll have some guys that stay year to year, but the higher end guys, the ones you use to sell merch and tickets will likely be up and down with NFL teams and tryouts and wouldn't want to sign long term deals. So can you exist long term as a sports franchise without knowing year to year what your roster is going to look like?
Buying in and being able to see some of those star College QB that the NFL doesn't rate well get a chance at a pro or pro-lite level and give them a chance to earn a shot as an NFL backup or something is intriguing. Guys like Tebow, or guys that get drafted mid rounds and get cut after bouncing around as a 3rd stringer. It could offer up a different path for teams to build.
Especially if it's successful and transitions to a league with an NFL agreement for development. Each team gets an XFL team as a minors system to help develop players on the edge? There are so many UDFA in the NFL that there have to be a ton of guys slipping through the cracks.