The final version of a contract is certainly PDF, but during negotiations, people must be able to make and track edits. Git has these features covered, but I just can't imagine sending a Markdown contract draft file marked "FOR DISCUSSION ONLY, NOT INTENDED AS A BINDING CONTRACT" to a typical counterparty.

I guess that your WYSIWYG editor might do the trick — it depends on the extent to which your counterparties rely on MS Office tools.