Having said all that, I recently participated in a conversation about EA putting ads in their games, and there was three different posts in three different communities, on the same subject.
I literally had to add links in my comment, that I was duplicating, to the other two duplicated comments of mine, so they were all cross referenced. It was definitely a pain in the butt to do so.
That's basically the hassle I'm trying to address (won't go so far as to call it a problem, just an annoyance). I wouldn't say I'm attempting to centralize things, just bring multiple conversations together into one view.
When I think of centralization, I think of something that makes the aggregation point a load-bearing facet. In this case, it'd just be detecting that there's 3 posts for the same item (from the cross_posts list from the API) and pulling the comment trees from all 3 into one UI display. Each still exists as its own, and nothing relies on the UI doing the merging.
That said, it wouldn't do much in your scenario unless other UIs did something similar (i.e. you'd still need to cross-reference you comments to accommodate other UIs that view them separately). It would just make it easier on you to participate in conversation on 3 posts simultaneously. I guess it would be a bit easier to cross-reference your comments since you could do it from the same page, though.