- it will need straightforward updates to work with the current versions of RabbitMQ Server, and
- it implements PSHB version 0.1 rather than the current 0.3.
Fixing the former would take about two days of expert work, and I don't know how much work fixing the latter would be. Both perfectly reasonable to consider, though.
RabbitHub is unique, as far as I know, in one respect: it uses PSHB as a generic webhook-based messaging protocol, rather than the more narrow Atom distribution protocol that the designers have in mind. There are other PSHB implementations, notably the reference implementation and Superfeedr, but they all as far as I know are specialized to Atom transport. A list of hub implementations can be found at http://code.google.com/p/pubsubhubbub/wiki/Hubs.