Thoughts on using 4NT

Hadn't posted in a while; no link to results for this one. A hand posted recently in a bridge discussion group inspired this:

You're dealer and open a standard 1C with x Jxxx Kx AKQJxx . Next hand overcalls 1S, partner bids 2H and your right-hand opponent (RHO) bids 2S. Partner's bid isn't game-forcing in competition, even if you play 2/1 GF normally; you'll lose out on too many part-score battles if partner cannot bid 2H with a nice 11 count. But your hand has only five losers and partner ought to cover three or four of those with his expected 10+ points. You should certainly force to game; what about slam? You can find out everything you need to know about slam with a 4NT Roman Key Card Blackwood bid: you are interested in the three missing aces and the King and Queen of hearts. But partner needs four of those cards for slam, and three to make a five level contract. You cannot be sure partner has three; 4NT isn't safe, sound or sensible. This is a common situation -- if you can suggest slam without forcing the bidding beyond game, trust that partner with a fist full of key cards will drive to slam. Here, bid 3S, a somewhat ambiguous game-force. Partner should initially assume you are asking for a notrump stopper, but when you follow up with 4H it should be clear you are suggesting slam. In some cases you might bid something like 3D; partner will think that's a real suit but again when you follow up with 4H partner should get the message you had more than enough for game. At first glance either 3H or 3C would seem to describe your hand better than 3D or 3S, but you should realize bids in "old" suits might be passed if partner stretched for his 2H call. In general, anytime you go out of your way to throw in an extra bid on the way to game, you are suggesting slam interest.