I don't think we're anywhere near that inflection point. The "best" locations for hydro may be taken (I don't know anything about hydro availability so I have no opinion there), but it's laughable to suggest that's the case (or nearly the case) for wind and solar.

I agree with you that once we run out of viable locations to put our renewable infra, it'll become more expensive, but I think you vastly underestimate the amount of space we have for that sort of thing.