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
Like a data format inhabiting the centre of that conversion graph they have on their website, basically a superset of the available input types, that is then version controlled by git, and can be exported to any of the output formats, in a neat frontend that removes all that complexity from me. :D