I ~~am sure~~ hope somebody™ already thought of this. Feel free to advertise your project here.
P.S.: Image transcription:
Patrick from SpongeBob SquarePants gesturing to the left with open hands:
Somebody should take document type conversion from Pandoc and version control from Git
Patrick gesturing to the right in a pushing motion:
And build a frontend around it
Shameless plug for Pandoc because I love it
That scalable vector graphic on the page shows source document type on the left and target type on the right. TL;DL: It converts about two dozen document types into about three dozen document types.
P.S.E.G.: PDF ← Markdown ←→ HTML → PDF
P.P.S: Where are my manners? Image transcription added to post.
The author is also involved in a markup language called djot, which is like markdown, but well-defined. It's an awesome language that will probably languish under markdown's dominance.