I did work in a district where the high school directors were trying to push MS to help their HS programs (the HS directors did help the MS for a few periods per day). However, it did not wind up getting set from the district level. The MS directors also had no assistants with large numbers. Mostly heterogenous beginners.
If the HS directors aren't asking for it, I would try to convince them to not push this. It could begin to cause a turnover rate if they have a lot on their plate. And like you, I've usually only seen this in small districts 4A on down in the metro areas.