I think there are 3 others; the Champions Indoor Football League (7 teams), the Indoor Football League (16 teams) and the National Arena League (7 teams). The IFL and the NAL have some former Arena Football League teams in them. The IFL already has an agreement with the XFL to be a "minor league" for it. And then there's the Fan Controlled Football League which is indoor but all the games are played at one place.
I had to look up some of that becaues I didn't even realize 3 indoor leagues still existed. So unless the AFL has some sort of backing like from the NFL or something, I just don't see it working.