I think the NCAA would welcome kids that don't have any interest in college going to the XFL.
As it is, I think most people's issue with the NCAA (as it relates to the amateur model) mostly stems from the NFL age restriction. If the age restriction is gone, then every kid that can be making money playing professional football, will be. Then any kid that wants to go to college to improve as a player and better their chances as a pro are welcome to. (Which is basically what college is about.) Right now, the NCAA is the best place to go while the NFL maintains its draconian age restriction.
If the XFL becomes a place professional level 18-20 year old football players can go instead of college - the NCAA would love it. Then it removes the major argument against the amateur model.
Statements made by Luck indicate they would be interested in going after college freshman and sophomores in the future. Still no indication that they would take kids straight from high school. This, in my opinion, would cause total chaos for college football to introduce one and dones.
I don't really know how this would work. With the AAF being a spring league, I don't really see it being feasible take a kid who's just a month so away from having played a full college football season and putting him into training camp for the AAF. This would also mean kids have to quit school mid-year. I guess you would play your freshman year, then sit out your sophomore year and pick up the AAF in the spring. But then once the AAF started their season, the kid will have gone a full year+ without having played football.