A BBF discussion got me to thinking.
This sequence has a lot of possibilities. I think a lot of these can be compounded into a multi-purpose bid.
Purpose #1: Exploration of minor contracts.
Responder might have, for this category of uses, one of several hand types:
1. Weak, both minors (5-5)
2. Invitational, both minors
3. Weak, with diamonds
Opener's first duty assumes one of these three purposes. With a hand that has prospects opposite the second option (Invitational, both minors), Opener bids 2NT. With lesser values, Opener picks his preferred minor.
If Responder had #1 (weak, both minors), he passes Opener picked minor or bids 3♣ (pass-or-correct) after 2NT.
If Responder had #3 (weak, with diamonds), he bids 3♦ (or passes Opener's 3♦)/
If Responder had #2 (invitational, both minors), he passes Opener's preferred minor. If Opener had bid 2NT, however, Responder now can bid 3NT, which is not a statement of a desire to declare 3NT but rather a descriptive bid ("I have both minors and invitational"). Opener looks at his spade holding, and uses judgment, to decide what to do about that development.
Note that this agreement as to the relayed diamond escape allows 1♥-1NT-2♥-3♦ to reliably show diamonds and values.
Purpose #2: Exploration of a Heart Game
Responder could always simply raise 2♥ to 3♥. However, to isolate spade shortness (make a short-suit game try showing shortness in spades, the most likely shortness in this sequence), Responder bids 2♠ and then, after any call, bid 3♥.
Purpose #3: Exploration of a Heart Slam -- Delayed 5-card Fit Bid
The prospects of a heart slam may initially sound slim. However, a slam is very possible. If Opener has 6331 pattern, for instance, Opener will have one suit controlled by way of that stiff. The need in that situation is the other three Aces, running hearts, and four more tricks. These additional tricks could come from a running side suit (Responder could have a 5-card minor) or a min-running side suit (a 4-card suit with all four honors) and the missing King. The HCP contribution for these two possibilities is about 22-26 HCP, which is easily possible.
♠x ♥AKxxxx ♦Axx ♣Kxx opposite
♠xxx ♥Qxx ♦Kxx ♣AQJx (26 total HCP)or
♠xxx ♥Qx ♦xx ♣AQxxx 22 (total HCP)
The easier to describe, and the strongest position, is the 5-card side suit scenario, as little is needed in HCP for a slam. With invitational values and a side five-card minor, with all prime cards (top three in trumps or the 5-card suit, possibly one side Ace), Responder bids 2♠, hears Opener's call, and then leaps to show his minor.
If Responder has no side Ace, he bids 4♣ or 4♦, naturally. If he has the side Ace of spades, he bids 3♠, and Opener, with interest in the minor, bids 3NT to ask for the minor. With clubs and the diamond Ace, Responder bids 4♣. With diamonds and the club Ace, Responder bids 4♥.
Note that 4♣ shows either no side Ace or the side diamond Ace. From Opener's perspective, strangely, the only bad holding is the possession of the diamond Ace. If Opener has a stiff diamond, he does not want Responder to have the diamond Ace, as this negates the value of the stiff and takes away some card Opener was expecting elsewhere. If Opener needs the diamond Ace, then he must, per force, have a stiff in spades, as Opener must have the stiff in one side suit to move. If he needs the Ace, then he must be able to tell that Responder has it after a 4♣ call because Responder cannot have enough HCP in his suit and trumps to get to invitational strength without the diamond Ace or cannot have only invitational strength with the diamond Ace. Thus, strangely, this creates a LTTC bid for Opener that seems counter-intuitive. If Responder bids 2♠ and then 4♣, Opener's 4♦ invites the slam if Responder does not have the diamond Ace. A strange but beautiful thing!
Note, also, that Responder might have a 5-5 minor heart slam try hand. If so, Responder may elect to show the preferred minor (if one is stated) as the fit-bid suit, or pick the one that is not Ace-empty. Maybe there is something better, but this is a damned good start, anyway. Leave me alone. LOL
Purpose #4: Exploration of a Heart Slam -- Delayed 4-card Fit Bid
As mentioned, a heart slam may also be available on a tight 12 tricks by virtue of a running four tricks in a minor, as well. The key is a stiff from Opener, again, solid hearts, a side Ace and King in the non-stiff suit, and a combined A-K-Q-J in a 4-card minor.
This puppy is tight. Not enough space is available if the heart game try option is kept. If not, 2♠...3♥ could cover a world of options. But, I like the Mini-Splinter. So, I'll limit this to one auction. If Opener shows a non-suitable hand and names a minor (3♣ or 3♦ after 2♠), this is the sole auction where a bid is undefined (3NT). So, we use 3NT to cater to that sequence, as a slam try that makes the most contextual sense. A slam makes the most contextual sense, in my opinion, if Opener has a stiff in the other minor. So, that is the Empathetic Splinter suit.
Thus, if Responder has a hand with invitational values made up of a decent four-card minor, no wasted values in the other minor, the Ace or King of spades and nothing else, and possible heart honor contribution, he can bid 2NT and then bid 3NT if Opener picks the "right" minor. This invites a tight slam if Opener does have a stiff in the other minor and honor help in the chosen minor.
Ah! But what if Opener picks the wrong minor? Responder still bids 3NT. Opener must cue if he has interest. Responder is captain. Opener cannot take over unless Responder cooperates in the cuebidding or bids LTTC. So, the "solution" is that Responder lies.
Yes, but what if Opener is rude and bids 2NT? Now 3NT has a definition, right? Well, in that situation, Responder fakes a side spade Ace. Heck -- he might even have it. But, when Opener bids 3NT asking for the minor, Responder bids 4♥.
You will notice that this fake 3♠ bid and then 4♥ offers an interesting twist if Opener has actually bid three of a minor. My thought is to use this to distinguish the possession or lack of the minor Jack. Without the minor Jack, I'd bid 3♠ and then 4♥ after a 3♣/3♦ bid. With the minor Jack, I'd immediately bid 3NT, the stronger and cuebid-enabling sequence.
I'm sure more or other things could be done. This is my idea to get y'all started thinking also.