Do any comment modules play well with revisioning?
I'm thinking out loud here... to simplify some aspects, I would probably try something like this first:


set up each 'revision' as it's own content
add a field that will follow each revision (ie. an internal product code that doesn't change even with revisions)
add a Views block to the bottom of the content page for that content type which includes a filter of ALL comments where those comments share the same internal product code but not from the current content - that way direct comments show normally, and then there's a view showing comments from the other revisions