Generalize to other modes

[fleimgruber]

While I was re-reading jorgenschaefer/elpy#498 (comment), I immediately thought about org-edit-latex and how one would go about to support editing Python docstrings in an org-edit-special like buffer with reStructuredText major mode. This would definitely be easier than the existing support for LaTeX, but I wondered whether you already thought about isolating the common bits to make them reusable for other scenarios where org-edit-special would be a good fit.