Which rabbanim are going to patrol and inspect women’s knees?
More seriously (though that’s nothing to sneeze at), I have NEVER heard ANYWHERE that four inches below the knee is a halacha.
Just saying, though, I don’t want no rabbanim inspectin’ MY knees.
Though if they decide to get women to do it, I know of loads of women who would queue up to join the knee-inspecting committee. To be honest, I don’t want THEM inspecting my knees either.
I’m going to reiterate what I believe, which is that while hochayach tochiyach is a thing, that does not extend (and definitely not in this day and age, where a Jewish governing body does not exist) to enforcement. A person’s decisions are their own, and they will answer for them after 120.
This is completely aside from all of the impracticalities of this plan (be honest, did the internet one REALLY work? The TV one definitely didn’t), but I still don’t think it’s anyone’s place to do this.