One thing that struck me the other day was that HN disallows commenting on items older than 2 weeks. This pretty much rules out the use case for me. I have been on the receiving end of intriguing comments that arrived after 2 years.
I would ask for Diaspora support, but after seeing that the comments will go through comments.network's infrastructure, I guess I'd rather not add that dependency.
Nice idea though, if you are cool with limiting comments to 2 weeks. I know some people do like that.