Posted 2018-April-08, 14:43
Well, part of what you do on this hand depends on how aggressive partner's "aggressive" preempting style is. If partner is apt to preempt at favorable vulnerability in 2nd seat with ♥ K109xxxx, then any ♥ contract beyond 4 ♥ could be in question.
In any case, I think you start with 3 ♠. If partner happens to raise ♠ like they should with 3, then I think 6 ♠ should have a reasonable play by drawing 2 rounds of trump and trying to ruff a ♣ in dummy if necessary.
If partner rebids 4 ♥, then the next question is "How would partner interpret either 4 NT or 5 ♥?" If 4 NT would be interpreted as RKBC/1430 for ♥, then that might be a possibility. Clearly, 5 ♥ over 4 ♥ has to be a how good are your ♥ question. But what will partner consider as good hearts? ♥ KQJ10xxx, ♥ AKQxxxx or ♥ KQ109xxx?
I think I'd more apt to use 5 ♥ after 4 ♥ and depend on partner to read that as requesting slam if partner can handle ♥ without more than 1 loser. (So partner would pass with ♥ KQ109xxx.)
BTW, I don't think it's clear that an immediate 5 ♥ is a ♥ ask rather than a further preempt.
Where a 4 NT keycard bid might help is if partner answers 5 ♠ (2+Q) and a further bid such as 6 ♣ invites 7 (with something like AKQJxxx.) But other responses to the ask are difficult to interpret what to do.
Finally, IMP scoring is such that not bidding a NV slam is less of an issue. If you don't bid it, but they do and it makes, you're down -500. If you don't bid it, but they do and it is set, you're +500. So bidding it or not is a wash.