markdown-mode in Emacs is pretty good, but it's not infallible. That said, it's impossible to handle all the dialects simultaneously.
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Today I learnt that Emacs 28 shipped a context-menu-mode! https://oylenshpeegul.gitlab.io/blog/posts/20230129/
This seems quintessentially Emacs: deeply hackable, but building UI features in an order very different to the mainstream.
One cute feature of markdown I'd not noticed before: there's no syntax for images *without* a description (i.e. alt text).
https://spec.commonmark.org/0.31.2/#images
I think you could build an interesting IDE with a tiny embedded LLM in addition to the usual tooling.
Features like 'extract method' would be much nicer if an LLM could provide a name. Choosing a good name is virtually impossible from just a typed AST.