In answer to your question, I would think probably never, or at least not likely any time soon. For all of the beautiful double downs I have seen in high school cheer, I have seen 5x the amount of scary, dangerous ones. I have seen more blood, busted noses and black eyes at high school competitions due to improper technique in double downs versus any other injury. I get that for the athletes that perform the skill well, it is frustrating not to be able to do it, but I think it is a stretch to say it is "degrading" high school to not be able to do them. It is a level 4/5 skill for a reason and shouldn't be done by the majority of high school teams.
To spin off this subject, I do wish that our state (not sure how other states do it) would set the divisions as novice, intermediate and advanced versus by divisions based on school population. Cheer isn't even run by the same organization that runs the other sports in our state, and it makes no sense to have teams that have level 2/3 skills compete against teams that have level 4/5 skills in the same division. This causes as much risk for injury since you have coaches trying to max out skills their athletes don't have to be able to try to be competitive in a division. If divisions were set on a skill basis, then I would have less of a problem with the double downs if they could only be performed by teams in the advanced
division.