I think this will have a huge effect all the way down to the bottom age of athletes, in every college sport.
Think through this scenario:
Let's say that at an average decent sized school, athletes - including walk-ons - earned $10,000/year. I'm using this amount because we have no idea how far reaching this will become once the market adjusts to the new reality. It's not impossible to imagine that with good fundraising and deal making, a college team could get a couple dozen sponsors and be able to pay a team of 20 people this kind of money, maybe a lot more. I don't know the limitations, but what is stopping Oregon from paying their men's cross country team members $100k a year? What kind of team will they have if they can raise those kinds of funds from sponsors?
Now let's say you're a parent of a high school athlete, who had previously thought it might be worth your time to encourage/push your child into a sport for a scholarship. I know a woman who has her son homeschooling and training like a pro swimmer with the expectation that he will get a scholarship. My kids do gymnastics with young children who are training 20-30 hours a week for future gymnastics scholarships. I think (before the NIL came around) that this is insane when you consider the cost of coaching; if they just put that money into an account there would be more money than the scholarship will end up being worth, and there's a huge risk the kid never gets a scholarship. This changes if the child is also getting some more money through sponsorship.
Some kids, like mine, have parents who are more on the bubble. I know the value of a scholarship but also the time commitment of running (I was a D1 recruited walk-on). I don't encourage my kids to aim for a scholarship because I can already pay for their school and I'm not sure the lifetime time commitment is worth the return of a scholarship. I'd rather my kids focus their time on academics so they can set up their future careers. I still encourage them to achieve their best in sports as long as they remain interested, but that's something on the side that's just a bonus, not the main focus.
Now, with kids, even walk-ons, potentially being paid to perform in college, as a parent I have to rethink to what level I encourage my kids to commit to sports in middle school/high school. I have a daughter who is just starting running but who appears to have a lot of potential. I'm almost certain with quality training that she can be a better athlete than I was, and with more scholarships on the women's side, she can probably get a scholarship somewhere. She wants to go to Stanford, so I look at that as a long-shot where she'd have to be a top 10 in the US talent (say 4:45 for the mile). Who could plan for something like that as though it were automatic? You'd have to be a fool.
With the NIL money coming into the picture, if walk-ons are getting paid significant enough money, doesn't that start to incentivize the girls who are more in the 5:10-5:15 mile range to stay committed and try to walk on somewhere (or take a scholarship at a lesser school)? I think so. And if this is the case, every parent who has a B-level talented child is going to push them just a little bit harder. They are going to put pressure on their kids' coach to make them that much better. Now it becomes economical to consider hiring a professional coach at the high school level because the payoff may be there for the child...you no longer have to be a top 50-100 in the US talent, you can be a top 200-500 talent and still get some decent money. There will be more professional coaches hired. Those coaches will feel the pressure to develop these kids faster (more mileage at an earlier age).
All of this will increase the level of high school competition. In turn, parents will begin starting their children into professional coaching sooner, like middle school, because high school became so competitive. The level of competition from top to bottom will increase. More talent will be identified. Times will get better.
There is a buttload of money out there and if teams begin learning how to fundraise, the pay for these athletes could get pretty significant.