>But who really likes Google Groups?
I'm trying not to be the guy who's overly harsh on someone for sharing a personal project, but this isn't really a relevant response to >>5's comment about Usenet.
If you meant "Usenet is unpleasant because you have to access it through Google Groups", then that's flat-out wrong, and missing the whole point of NNTP.
If you meant "Usenet is unpleasant because some other people somewhere access it through Google Groups", then I don't think any software is going to solve your problem, and certainly not decentralized software.
So, what you're describing really sounds a lot like NNTP. It's distributed, threaded conversations, thread classification is many-to-many form, and so on.