Its fairly common to use markdown as shortcuts to WYSIWYG content - Obsidian and Notion for instance. At a higher level at some point if you want a fluid typing experience, you need some form of shortcuts, and given markdowns conciseness and ubiquity its a good choice as opposed to having a proprietary format users need to learn for just your app.
+1 - a universal way of doing this via markdown beats learning whatever app-specific hotkeys I have to do to make an H3 or whatever. I don't have any particular feelings about markdown as a format for data, but as a universal set of shortcuts, I've found it to be a huge productivity boost.