As long as they are clearly flagged as old content, then what’s the harm (note that this might just be a reasonable use for large section heading fonts in comment number 1).
If people have nothing (new) to say about the post, then the contents would remain empty, if they do, well, it’s interesting discussion – even if/especially if it’s commentary that’s only made possible by the hindsight available in the time since the article was probably posted. (“Oh yeah, $TECHNOLOGY, really did change the world and cause the Singularity, didn’t it?”, “What would have to have been done to make Google Wave work?”, that kind of thing. ) This itself would be interesting to me. 
The only big issue I can see is the that people might think that this is new news, and well, a clear notification in comment#1 would mitigate that.
(Hell, having been fooled myself at least once by the old-content retweets on Twitter, the ‘Old post’ warning text on the BBS could actually help unconfuse people when they click through to ‘the comments’?)
