I wonder if 4NT directly should just be 6-key RKC, leaving 4H for something else, such as "answer keys only if you have first or second round control of hearts" (starting with 4NT as first step with heart control, but bidding 4S without). I don't think so because 6-key RKC is most helpful when you have a double fit and both of you have length, but that is not really the case here. The person trying for slam could easily be doing it based on shortness in the second suit and long trumps, in which case he might not even care about the king in the second suit let alone the queen.