I also had experiences with mixed skill level classrooms and frequently found myself paired with students who didn't want support -- either from myself, other students, or the teacher. They didn't want to be in a classroom of any kind. I can imagine environments where this does work, but it freaks me out a little bit that you say you're certain this works.

As an additional anecdote, my son loves his gifted classes. But similar to myself, that's where his friends are.

I wonder if we'd both agree that kids' social environment is more important than the structure of any particular learning program?

This isn't true of everyone, but assuming it is increases the likelihood that it will become so. Because if everyone is trying to get away with it, why shouldn't I? That sort of breakdown in trust is high up on my list of worrying societal failure modes.