I mean when I was in school for a few grades some of my teachers assigned Khan Academy so it was basically that.

I don't think it worked well, but honestly I can imagine a good teacher just replacing whatever course material they're using with KA and lecture off of it, while still somehow incorporating classroom interaction

That sounds like the worst of everything - you won't be getting the benefit of having someone who can explain things to you in person (kind of wasting a teacher) and you also won't have the opportunity that KA gives you to take things at your own pace.