Is there an easy way to write Latex (e.g. with MathJax or Katex)? That is for me the most wanted feature of Medium (my intuition is they won't be adding it any time soon).
If it supports inline HTML (not entirely clear to me), then you could try using markdeep[0] to render HTML offline, then copy the output to the editor.
EDIT: just tried, does not work without KaTex being loaded