Original: Your Org source
A: Org -> DOCX for co-authors (using pandoc)
B: Org -> DOCX -> Org (using pandoc).
C: A -> Org (using pandoc and --accept-all-changes)
The difference between B and Original are pandoc-introduced changes that you do
not want. Ignore/remove these changes from C, call it D and then the difference
between D and the Original are your co-author comments. Now your authors can
edit DOCX with Track Changes and you can work on those edits with Emacs ediff.