It's written in an experimental language, as an experimental side project[0], on a single machine in...I like to think it's PG's basement.
Considering this, it's probably not a service that can be "open sourced" as the number of people who can actually work on it appears to be PG. And PG is probably too busy to even act as the project lead.
YCombinator is listed as in the Rackspace Startup Program [0] - I'm on my phone so I haven't had a chance to do due diligence, but is HN hosted on a Rackspace server?
Considering this, it's probably not a service that can be "open sourced" as the number of people who can actually work on it appears to be PG. And PG is probably too busy to even act as the project lead.
[0]: It's not so experimental anymore...