OK, so we all know that a 1D opening can mean about anything, with just about any number of permutations for when and what.
How about minor rebids? Those who debate ad nauseum about the merits or lack thereof of some particular tweaking of 1D versus 1C as an opening do not seem to have as much to say about minor rebids after a major opening after a forcing 1NT response.
Seems rather obvious? Better minor? Why?
It seems to me that there is quite a bit of play available here.
Some, for example, require at least 4+ in diamonds to introduce them. This would, in the case of a 1S opening, tend to promise 2+ clubs for the 2C rebid (the 5332 situation). What about after a 1H opening? With 4531, 2D, or 2C? How strong are your (and partner's) convictions here? Does the 4-card rule (if you use this) apply only in the event of a 1S opening? Does your use of Flannery allow the 4+ agreement for 1H openings? Is that concern a plus for Flannery (negatives exist, but a plus does go on the plus side)?
How about minor 2/1 calls? 1S-P-2C or 1S-P-2D? If you assume 5+ for hearts for bidding 2H, then a non-fit minor call must have at least four (2434 or 2434). But, against this you could, first of all, opt 5+ for diamonds and a possible short club, even in the no-fit scenario. some, therefore, mean "real diamonds" for a 2D call, but 2C shows either "real clubs" or any balanced.
Of course, other permutations seems plausible. For instance, in the non-fit scenario, it seems plausible to have 2D mean "real diamonds," meaning "a hand with which I'd open 1D," meaning possibly 4+ but only if unbalanced, for example. I am sure that many permutations for no-fit scenarios exist.
Add onto this the "with fit" scenario, where the 2C call (or 2D perhaps) is solely to establish a GF before raising Opener's major, because a 2/1 sequence seems best (or is the only option). In that event, you might find that a minor response is wildly unknown. I mean, with 4-5-2-2 pattern, I'd respond 2C often, whichever major was opened, because I'd want the GF and all the benefits that this brings.
Finally, what about jump shift minor rebids?
1H-P-1S-P-3C or 1H-P-1S-p-3D, for examples. Either could be "artificial." With a very strong 1-6-3-3, where you want to force game not, what else? Or, 3-6-1-3/3-6-3-1? Well, if both are available, is one "real" and the other "suspect?" If 1H-P-1S-P-3D promises 4+ diamonds, then 3C in that sequence could easily be a stiff (3-6-3-1).
I would suggest discussing general principles here, with partner, and specific instances.
I remember hearing that someone noted how we lost the club suit years ago, and the diamond suit is fading quickly. (Who said that, and what's the quote?) Well, maybe we should discuss precisely what this means? some of you may want to save diamonds, knowing that clubs will be hit even harder.