A situation I have not thought of before popped up on BBF.
Grand Slam Force is so obscure here. Responder cannot have that hand.
However, I could see merits to splitting "hands with void in hearts" between 5H and 5NT rather than simply having 5H as Exclusion, because Exclusion might be too much.
It seems that structurally, one could figure out the "problem key cards" situation. Let's say, for sake of argument, that the answer "two key cards" is the problem response, where slam won't make. With that hand, Responder bids 5H, allowing Opener to sign off with two key cards.
With one better than that (two key cards works), Responder bids 5NT instead, which is Exclusion RKCB, void in hearts.
But, better could be done. If Opener hears 5H and has exactly that needed for slam opposite the hand shown by Responder (two with the queen in the example), he bids slam. With three and the queen, he answers specific Kings at the six-level. With three but no Queen, he bids 5NT.
Make this even more interesting. If two without works for the grand, Responder could bid 5H anyway, expecting a 5S rebid by Opener. After this, 5NT by Responder could then ask for specific Kings, which saves space.
Exactly how to structure this is something I don't feel like working out right now. Furthermore, I have not thought through the most likely problem answer spot or most workable problem answer spot. But, the idea of sort of a Culbertson 4NT/5NT conventional mechanism for handling the one-under "Exclusion" call, with the addition of a 5NT call, seems workable.