[JLilly]

One of the drawbacks to a semi-forcing 1NT response to 1M is that responder with a weak hand and a long suit can't bid 1NT and be assured that they can get out in their suit. 1NT played by responder with something like xx x Qxx KJxxxxx opposite a flat minimum opener could be disastrous. In thinking about how to accommodate the semi-forcing NT in the context of a 2/1, strong NT that a partner and I play, I was thinking of using 1H-2NT as this hand. It fits with a response structure to 1H that uses 2S as the unlimited balanced raise, and with 3m either as natural and invitational or to express various limited raises especially the three-card unbalanced limit raise that can no longer go through a forcing 1NT response.

I'm thinking this is suitable mainly in response to a 1H opening rather than a 1S opening, because (1) a weak jumpshift has more value when opps could have the master suit, (2) an unlimited balanced raise of 3C to 1S leaves too few steps for the various Jacoby structures (standard, Swedish, whatever flavor you like), and (3) we have the impossible 2♠ to distinguish a invitational long-minor hand from a courtesy raise of opener's 1♥-1NT; 2m rebid.

So the response schedule is:
1♥ - 1♠ = unchanged; may want to use some science to address that this response has to hold every responding hand with spades, since 1♥-2♠ is no longer available as an intermediate or strong jumpshift.
1♥ - 1NT = semi-forcing. Does not include weak hands with a long minor.
1♥ - 2m = normal 2/1
1♥ - 2♥ = normal simple raise
1♥ - 2♠ = balanced GF raise or balanced lim+ raise
1♥ - 2NT = weak jumpshift in a minor. Opener usually bids 3♣ pass-or-correct; can bid 3♦ with a hand that would bump a natural 3♣ bid to the four level.
1♥ - 3m = natural invitational, or, I think better, limited raises of opener's hearts, such as a 4-card mixed raise and a 3-card unbalanced limit raise.

The invitational 6+ minor hand can be shown after 1♥-1NT by bidding it at the 3 level over opener's non-fitting rebid or using the impossible 2♠ if opener's rebid hits it. What do you think, BBO?