Markdown support would be great to highlight important parts of the text in between lines.
I don’t think Markdown makes any sense in a WYSIWYG editor. Aren’t the available formatting options and shortcuts enough for highlighting?
Support for importing and converting Markdown formatted content would be extremely helpful for all those users importing csv files and using x-callback URL. I would do most of my text formatting outside Anki then and save a lot of time.
But formatting is already available through HTML. Why not use what is already available?
Perhaps OP didn’t mean highlighting specifically, but rather editing as a whole? I feel like Markdown is the perfect match for Anki, because it is super fast to edit and remains readable cross-platform, in CSV and other formats.
How about a separate field mode for Markdown? It would need to be one-way though, like the forum editor here.
Edit: CodeMirror supports GitHub-flavored Markdown, so it could be as simple as adding an option in the fields dialog for Markdown instead of HTML, then loading the CodeMirror instance in GFM mode.
However, ideally we’d offer users the choice between WYSIWYG and plain text, like they have with HTML. ProseMirror seems to be better suited for that: ProseMirror markdown example.
Markdown: Easy to edit, good readability, widely supported in a lot of text editors and other apps.
An observation: I do have an addon (which is at the moment not perfect: Markdown input - AnkiWeb) that does exactly this: you can toggle the edit fields to markdown or open a separate window to input markdown. It uses CodeMirror 6 and micromark/unified for conversion and what is stored in the database is HTML (so it will work in any reviewer). One of the outstanding issues is how to integrate the field mode with Svelte (as asked here: How to correctly add additional editingInputs) for better functionality.
The current visual/HTML editors make sense because each can be losslessly converted to the other. Markdown is considerably more difficult - not all HTML can be represented in markdown (except via embedded HTML), and the conversion process is intended to be done in one direction.
Robust Markdown import is nevertheless the only practical way to import preformatted text. So a one direction conversion (Markdown is intended to be converted to HTML, not vice versa) when importing/initially creating notes (e.g. through X-Callback URL) would be sufficient for
my most needs.