I see some professors use pen tablet input on computer slides during a lecture. This is similar to what you describe for overhead slides. In practice, they also seem to use it for the things you describe for the chalkboard.

My favorite video lectures are Gilbert Strang teaching Linear Algebra with nothing but a piece of chalk and a whole lot of chalkboards (the kind that slide up and down, revealing other chalkboards underneath). I can't think of any way those lectures could be improved by any sort of technology.