Hi,
I think more and more people got used to at least the basic use of markdown. I think for the workflow markdown can be more convenient and less disruptive then the normal rich text editor. I know there is a extension for that but is has limited features i.e. you have to convert your formatting manually by clicking a button.
Markdown is always universal, so there's no need to look for the right option/button/shortcut and it has a lot of "extensions" like mermaid which are really really helpfull. Maybe some people would like to see a markdown support for their mail-client, at least I would love to as I'm using markdown frequently and love how convenient it is.