The first elisp client was created two years ago, and since then I haven't really seen much more. In principle, it's probably not needed in the usual sense. It would be better to integrate nostr into org-mode
I was mistaken, it's not even written in elisp, it's in Python. I forgot that people now write for Emacs in all sorts of languages.
I think I found that one. It used Python to do the cryptography, but the actual client was still in elisp. Something more recent could be cool to play with. I would rather expect a Gnus extension fits better than Org mode.