There has been some debate between the classic responses to a 1C opening, Walsh responses, and Montreal Relay. One modern innovation is toward "T-Walsh" or transfer Walsh. So, could one, then, imagine and use yet another approach, one that might be called "X-Montreal," or cross-Montreal?
1C-P-1D = no 5-card major, typically a 4-card major.
1C-P-1H = 5+ spades
1C-P-1S = 5+ hearts
Let's play this out even further. First, start with the spade sequence. 1C-P-1H. Responder has 5+ spades. From his side of the table, he could later bid 2H or 3H, as appropriate, to show a spade-heart two-suiter, longer (or equal) spades. So far, nothing really sexy happens, except that Opener can bid spades first, which may in the long run be better for lead reasons. The normal raise method could be 1C-P-1H-P-2S. Not a jump shift -- just the normal raise that would have occurred if Responder had bid 1S instead of 2S.
What about the heart cross-over? 1C-P-1S. Responder has five hearts. Again, everything works out fairly normally. Opener raises normally but grabs declarership. 1C-P-1S-P-2H.
You then might be thinking that there is a problem in the 1C-P-1S sequence, in that Opener cannot bid spades. In the 1C-P-1H sequence, however, the auction is in theory improved, if Opener's 1S call shows hearts. You end up with an easy auction (Responder has spades and hearts and could normally bid 1S and then 2H) being made even easier and better (Opener can show the hearts himself below 1NT, allowing Responder's 2H to show 5-5). But, you end up with the easiest normal auction (Opener shows four spades after Responder introduces hearts) becoming what appears to be unworkable (the 1S call preempts the ability to show spades below 1NT, and Responder cannot later introduce spades without a reverse).
However, that perception of a complication is perhaps mitigated by that fifth card in hearts. When the auction starts 1C-P-1S (Responder has five hearts), Opener either started with (1) a balanced hand or (2) an unbalanced hand with clubs. If balanced, 2H is often the best contract anyway if Responder has a weak hand. I mean, with five hearts, is the normal auction often 1C-P-1H-P-1NT-P-2H anyway? So, let's start with the idea of Opener raising hearts (1C-P-1S-P-2H) with any balanced minimum hand (not the 18-19 balanced hands). Is this, so far, workable?
Fairly so. Responder will often bid just like he would after a transfer to a weak 1NT opening. Opener will be allowed to make calls that confirm a true fit and calls that show shortness. The opponents, if 2H is the final contract, will not know if the fit is real or not. So far, I could live with this.
Back to Opener's problem at rebid. Suppose Opener is unbalanced. Because Opener will always rebid 2H with a minimum balanced hand, 1NT must, per force, show an unbalanced hand. So, let's define that as promising four cards in spades. Non-forcing, but this would carry a strong encouragement to not pass, as Opener might have a fairly strong hand. If Opener has four spades and a balanced hand, with only two hearts, he could opt to treat this as "unbalanced" and bid 1NT, prepared to bid 2H later if necessary.
What bid would be left out? If Opener is unbalanced, without four spades and without three hearts, he has at most 5 cards in the majors. If diamonds are short (hence the unbalanced hand), Opener has 7+ clubs and has an easy rebid. If spades are short, with only two hearts, again Opener has 6+ clubs and an easy rebid. If Opener has precisely 3-1-4-5, 1NT to show spades is not implausible, nor is opening 1D instead (if that is your normal style), nor is rebidding clubs. Strangely, a similar problem to other methods.
So, it seems to me that the five-card suit allows Opener to support hearts with a doubleton and to dedicate 1NT to unbalanced (or balanced with 4-2 in majors), so as to mitigate the problem sequence for a "X-Montreal" approach.
I am not sure whether this all would have any net benefit or loss. I have only started to think along these lines. But, as I am unaware of anyone tryig this method before, and as it seems workable, I am rather curious about the concept. I would enjoy any feedback.