From a discussion on BBF:
Opener: ♠Axx ♥Ax ♦KQJx ♣KQJx
Responder: ♠KQxxx ♥xx ♦Axx ♣Axx
As you can see, agreeing spades, having Opener bid 4NT as RKCB, and getting "three" and then "with the Queen" makes bidding 7NT (13 top tricks if spades behave) easy. Add the spade Jack to Opener's hand if you want.
However, after a 2NT opening by Opener, this task is more difficult and resulted in the discussion.
My initial thought was that this is a good problem explaining why 3-card super-acceptances after a 2NT opening make sense, IMO. If Opener can set trumps immediately, such as with a 4♣ cue, Responder can reciprocate with a 4♦ cue and we are off, well-placed to bid this hand. The risk is in reaching 4♠ without much play, such as opposite trash on the outside and weaker spade honors. However, that risk seems somewhat worth taking, because of cramped space. After 1NT and a transfer, Responder might have options like three of the other major or a fake minor or a splinter to get things headed in the right direction. Nothing is available over 2NT below game if Opener does not super-accept.
An interesting alternative, or an additional tool if you will, was suggested by "pclayton" as from Meckwell, apparently per Walter Johnson, namely that a transfer followed by a five-level call by Responder is immediate RKCB answering. I assume that 3♥...5♣ would show a five-card spade suit with slam interest and 3 key cards, 5♦ then as a queen-ask, whereas 4♥...5♣ might be the same start but with six+ spades. Not sure. I'm also not sure precisely how Opener gets out at 5NT if that is right. Presumably 5NT is to play, whereas 6♣ might be the specific King ask.
This seems workable. It gives up on Exclusion, but that seems rare. Maybe Texas and then the five-level is Exclusion? Not sure what Meckwell does or what makes sense. I just found this idea interesting. I have used similar concepts myself in some sequences, and I have even found the usefulness of occasional calls that demand that partner ask. This seems like a good solution for a difficult problem.