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.