I don't use emacs, so an emacs mode isn't that useful for me.

Org-mode stuff can be authored outside emacs. There's even a Visual Studio Code addon for it. And pandoc groks it.

But yeah, to unlock the true power of org-mode you need emacs.

Org is also just a file format with extensions available in VS Code, vim, sublime, and Atom. I've personally used the VS Code extension, I think it works just as well as the Markdown extension.

[1]. https://orgmode.org/install.html

It's not just a doc format though, it's also a task manager format, a literate programming format, an everything format with no clear separation.

I can't help but feel like it would be a lot more widely accepted if they divided it in multiple projects each with their own goals and requirements.

That is a much more challenging task - even if they had planned it from the get go. One of the reasons people gravitate to Emacs is that it is much easier to build integrated systems like Org mode.

The other barrier, of course, is that it doesn't really benefit existing Org mode users/developers.

GitHub’s org-mode support for README files was so broken that I just gave up the last time I tried, about a year ago. Is it better now?