What I'm imagining is a page with comments from both sites (no doubt with the source marked with a stripe or an icon or something) with the threads in order of posting. (I'd like unthreaded [new|old] as an option, too. And a pony.)
I'm not sure whether this is an option best activated by the reader or by creator of the post, or as an option for both.
I'm inclined to think this would be a lot harder to maintain the conversation for flocked posts because some people might have permission to read at one site but not the other, so lets assume it's only available for public posts.
If it's possible at all, I assume it would also work for deadjournal, insane journal, and anyone else who's using the same software.
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