+1, would make copy-pasting paragraphs easier too.

Implementing it with tab style (Smart editor, Markdown) makes sense IMO

We need to check how it works in regards to normalization with the editor (what happens if we edit the markdown, it's invalid, we change to the WYSIWYG editor, and back to the markdown editor -> what breaks ?)

Would it actually be required to switch back and forth though? Surely having a markdown option that you can't switch between would be better than none at all - select at start, or have a checkbox in settings to enable the option so people can't accidently stumble into it?

No switch is fine, but having a preview tab is needed. Much like the one we're using rn on the gh front.