dvcs-autosync is an interesting project
The OPs question IIUC is orthogonal to it.
The problem as I see it is that org mode docs are two things:
-- they are text mode data (when in emacs mode)
-- hierarchical data (when in org-specific mode)

Diff  unfortunately does not understand the hierarchical view.

I tried to see if xmldiff will run
And if it did then try pipe the output of org-docbook-export to it.

Unfortunately my attempts at getting xmldiff to run did not work