org-mode already has this. Unfortunately, people seem to continue to use the inferior version of org known as Markdown. It is somewhat like how pdf overtook the superior format djvu.
Unless using Emacs becomes a user friendly beginner's choice (which it isn't, and that's fine) or Org is able to distinguish itself in isolation from Emacs, I don't see org being widely used anytime soon. If org gains first class support in editors like neovim, vscode and tools like pandoc, mdcat etc, I could see myself using it.
I built two apps for iOS:
There are other org-based tools out there.