I would be interested in someone trying out creating a plugin for something like GitHub - guardian/scribe: DEPRECATED: A rich text editor framework for the web platform · GitHub , that said the concept of markdown is baked quite deep into Discourse and HTML to markdown engines are all fairly rough.
I don’t see much room moving to StackEdit as we own our editor and markdown pipeline and are constantly adding the features we need to it. We have the architecture to allow for various extensions that stack edit has.
I find CKEditor and the rest of the bohemouth do everything wyswig editors a pretty big problem, but sure people can create plugins.
Transitioning in and out of non-markdown editor plugins will be a massive pain though.