One thing my partnership stresses (and I recommend to others, not just who play weak NT, but any "off-standard" system) is "what will the world do? and why should we not join them?" Note the emphasis. Just like a good "default question" is "are trumps out? and why am I not pulling trumps now?" (obviously there are many, good, answers to that question, but unless you can find one, pull trump now) I believe that there's enough variance playing a non-standard system that unless there's a very good reason, I don't want to increase it. In the homogeneous world that is ACBL club bridge, doubly so.
It has to be "the information we got from the system tells me that the standard pattern is likely wrong on this hand" to walk away from it - because you're playing a full-board gamble when you do. Now you might be coming from a full-board gamble situation already (which hand has the killing lead?), but you might not. Really, "wrongsiding" isn't as big a deal as it's made out to be. In my opinion, the losses from "playing the major from the wrong side" are far outweighed by the losses from "playing a different contract", and "letting the opponents in at the 1 level" (of course, the gains from "playing a different contract" and "not letting the opponents in at the 1 level" do compensate).
As an example, "we freely bypass one, even both 4-card majors to rebid 1NT." The room knows that opener has a balanced 15-17; making a second call that denies that critical information to responder doesn't gain anywhere near enough to catch up.
Here, the auction in the room is very likely to go 1NT-2
♣; 2
♠ or 1NT-2
♥;2
♠. Whether it's right, wrong, or wrandom, almost without exception (1NT-p, or Stayman, then 3
♠-3NT "choice of games, I'm flat"-pass seems like the most likely) the field is playing in spades. You want to play NT instead because it rightsides the contract and you're square; hoping at least that if partner has 5, they won't pass you - that depends a lot on how often you raise on 3, I guess. Let's look at how we answer my question with this want.
At IMPs, a lot of the gamble is "will NT go down where partner's trumps are the extra stopper?" And if partner raises you to 3NT, it's a pretty big gamble; if it's just 1NT, it's still 4-6 IMPs if you lose. Of course, you might make the same number of tricks as the spades players, and it might be 7. Of course, you might make one fewer trick than the spade players if your partner has to play spades because your hand is on the table, and if that's 7, your -4 in 2
♠-1 just became -1 in 1NT=. But that's your gamble.
At MPs, a lot of the gamble is the default "everyone is in spades, I'm actually *playing* 2NT here" that you're used to from 1NT-p. How do you feel, when dummy comes down and you know everyone else is making 110, so 90 is almost as bad a score as -50? Is that something you want to do more of? For me, that's a "not really, not if I don't have to". Similarly, "I'm actually playing 4NT here" when partner raises you to game "knowing" there's no spade fit.
One more gamble, of course, is "how much do you damage further auctions by violating system this time?" Assuming you don't agree that 4333s will be treated as 3333s, now partner will wonder with their nice 4144 next time "do I check back for partner's *4-card major*, just in case? What will partner do if I do check back?" Okay, maybe they won't do it. Maybe the partnership is strong enough that stepping out occasionally won't trigger doubts about another step-out. But maybe it's not. Assuming you *do* agree that 4333s are treated as 3333s, what do you have to change in your system to handle it? What downsides do those changes have?
So, in my opinion, 2
♠ it is.
Why 2
♠, not 3
♠? Because the 12-14 NT isn't a "killer weapon" that "destroys the opponents" (although it is quite pre-emptive, and it does give the opponents some unsolvable problems nobody else has). It's because, just like the strong NTers use that bid to acquire clear separation between "bad balanced openers" and "very good balanced openers", and build the rest of their system around that, the weak NT allows us to know that when we open 1m, *we don't have a bad (semi-)balanced opener*. And frankly, in order to use this effectively (K/S, North American style; as always, I can't speak to Acol, because I have not investigated the decisions they've made to understand how it
can possibly works.), that means that your 1m openers have to be sound, with minimal exceptions that are clearly understood.
And that means no random 4315 (or 3415, and especially not 4135) 11 counts. Those have to be passed. Yes, that is an issue - one MikeH has stated here recently, he believes is effectively a death-knell for the system at highest circles. Yes, there are hands we've passed out that made game in the room. But it means that when you show one of those "not minimal exceptions", it means you have the goods.
In K/S style, North American weak NT system, 1m-1M; 2M is "promises 15-17 points in support of M. Might not have it, but that's what it promises." And 1m-1M (2x, or double); p is "assume partner has a strong NT that can't raise you". And this is a *huge advantage* when you get to do it, and makes up for a large amount of "wrongsiding", "letting the opponents in at the 1 level", and all the rest of the system losses you get. And it means when you jump to 3
♠, you've got even *more*, and you won't be concerned that partner will pass with enough for game (the way strong NTers have to decide whether to "upgrade" their balanced 19s into game, just in case partner passes a useful 7 opposite the "good 15-18"). And it means that when you jump to 4
♠, partner doesn't have to worry about going down in 5 opposite that "good 18 or balanced 19" versus missing slam with the 21 or nicely shaped 20 (or did they decide to move those into 2
♣ openers because they've missed too many slams?)
If you throw all that away, you're operating from behind, in my humble opinion. You have shown parts of your system agreements before that says either "we don't understand what our 1m openers look like" or "we are choosing to throw that all away". The first case is "Read the K/S book, and then review your agreements" (maybe start with KSU and decide what you don't like about it and why?); the second is a very good reason to abandon the weak NT and all of the hassles and forced variance it gives you in favour of going with the field.
When I go to sea, don't fear for me, Fear For The Storm -- Birdie and the Swansong (tSCoSI)