"VexTab is a language that allows you to easily create, edit, and share standard notation and guitar tablature. Unlike ASCII tab, which is designed for readability, VexTab is designed for writeability."
all textual representations of data are "formats" and one being easier to edit is a totally valid use case. like 'x57675' instead of a full tab. or # title instead of <h1>title</h1>
Not really. The lilypond format is extremely...complicated and obscure (and that's my polite take on it). Even simple stuff is quite complex. Very very far from Markdown's virtually WYSIWYG.
Yes, but music notation is not simple text. Markdown was made for simple text. If you try to represent more complex text, it turns into Asciidoc or Rst.
https://vexflow.com/vextab/tutorial.html