This looks like something I would love to have for myself, but I have no idea if the Nanowrimo site where I use Discourse would provide it for one oddball user from the antediluvian past.
As a touch typist since 1984, and an emacs user since the mid 90’s, I’ve got the keyboard motion commands wired in, and there is an effort involved that slows me down when I have to stop my reflexive attempts to do the emacs thing in a Discourse edit box.
But, as I noted, I’m an oddball.