This isn't much of a request, but I figured it may be a valuable question to ask and I thought this was the best possible place to ask it:
concerning what you've already mentioned regarding the character limits of your codes like you mentioned with blank dominoes here, have you considered also making a separate series of non-natural codes that would include the trickier ones (like CRD### for playing cards, DMN### for dominoes, etc.)? I'm sure there's also a good reason why you wouldn't implement it, but I figured it was worth throwing out there; at best it would require additional information in your primer doc, which isn't a bothersome extra step for designers, I think.
Good question—the answer is I'm keen to keep things consistent throughout the typeface, even if it means losing some edge-cases. For something like Dicier I'd prefer fewer features done more reliably and accessibly than the other way around. With the domino blanks in particular, I can add the missing icons using OT character variants—the only thing Dicier'd be missing then is the codes.
One thing about the character limit that gives me a bit of hope is that there are scripts with very long ligatures (e.g. Arabic), so hopefully more and more apps will support longer ligatures in the future.