HTML is good for layout, but bad for formatting. Markdown et al. are good for formatting, but useless for layout. WYSIWYG-giness is not a part of the problem, you can have WYSIWYG editor for markdown.
> At some point you will have to allow raw HTML and JavaScript to be embedded within it
{{citation needed}}
> There are a few benefits that markup provides over a decent HTML editor - certain changes can be more semantic, and it's easier to diff
You forget about indexing and sending plaintext emails. You'll have to do something about soup of tags surrounding a typical WYSIWYG-generated html.
Besides, you don't need to think about sanitization and malicious inputs: markdown output tends to be mostly harmless. You'll have to disable inline html and custom element classes, though, otherwise it might break your page layout.
> At some point you will have to allow raw HTML and JavaScript to be embedded within it
{{citation needed}}
> There are a few benefits that markup provides over a decent HTML editor - certain changes can be more semantic, and it's easier to diff
You forget about indexing and sending plaintext emails. You'll have to do something about soup of tags surrounding a typical WYSIWYG-generated html.
Besides, you don't need to think about sanitization and malicious inputs: markdown output tends to be mostly harmless. You'll have to disable inline html and custom element classes, though, otherwise it might break your page layout.