@KitRedgrave in more length: ZWJ basically means “form ligature here”. thinking of 🧑‍🌾 as a ligature of 🧑 and 🌾 kind of makes sense; it’s certainly not the most elegant solution, and it was chosen more for political/temporal reasons than accuracy ones (basically, vendors wanted to add a bunch of emoji without waiting for the next Unicode release, and it was questionable whether a lot of those characters would pass muster for atomic encoding anyway. so they defined ligatures between existing characters, and Unicode standardized those).

but the demicolon isn’t a ligature of two semicolons (it doesn’t have the same meaning, and if you showed someone a demicolon, they wouldn’t say “ah yes, that’s two semicolons right there”). plus, forming ligatures from punctuation marks like that doesn’t have any precedent and would be difficult to document. (emoji have a separate data file of sequences, but that’s generally not true for ordinary characters.) it’s its own punctuation mark, so an atomic encoding is best.

that said, there is no rule against fonts encoding their own ligatures above and beyond those defined in unicode. whether encoding demicolon as a ligature of two semicolons is preferable largely depends on what fallback behaviour you want if the font isn’t installed: is a fallback of two semicolons desired? or would you rather use a private‐use character, and make it explicit that it’s not a character with an assigned codepoint in the unicode standard?

@Lady honestly i just wanna post it as a one-off for dumb funposts and have others see it

@KitRedgrave unfortunately the best solution for that in 2021 is probably <del>embedded SVG</del><ins>custom emoji</ins>