We already have a site for that, it's called Reddit. I get the impression that most HNers are also Redditors, so doing AMAs on Reddit makes more sense than trying to make HN into Reddit.

That was sort of the point, except that it doesn't stop people from wanting a higher level of discourse/participant on Reddit or more Reddit features on HN.

If anything I its 50/50 (overlap/strictly-HN), and I think that's being generous.