As I said, optional at all levels. Let's look at what we're actually talking about:
Setting NCAA aside, you would start by having the NFHS change Section 1 Article 1. Instead of only allowing singlets, allow for an alternate uniform such as fight shorts and compression shirt. At that point, every high school in the country would choose which way they want to go. If it turns out most kids want to keep singlets, then most schools would keep singlets and the alternate would fade away. If most kids want the change, most schools would change and high school wrestling would have a new look.
The thousands of youth organizations would be free, as they are now, to set their own rules. Of course, most of them use the NFHS rules as their guideline, so if high schools make the change most youth programs probably would, as well. But it would be each club's choice.
If what you're saying is true, and most youth programs in your area don't require singlets, then I'm not sure why you care. It's not like we're advocating armed mobs swarming into the youth practices forcing fight shorts onto them!

And your current shorts/t's is much closer to the new look than they are to singlets -- you're practically using what I propose already!