Our project http://www.oarinz.ac.nz
is looking at using the PKP harvester2 as a integral part of the network. The role would be like a hub -> sub hub -> Institutional Repository. I really like the architecture of the Harvester and the plugin flexibility is great. To that end I am developing a OAI out plugin that exposes the harvested data to be harvested by other harvesters.
The project also is looking at devloping a number of other plugins
General Plugin -> SRW/U exposure
Post Process Plugin -> Validation of harvest against predefined standards e.g "At least one Subject" this will feedback info to Repository Admins about how they can improve data in their repositories
Post Process Plugin -> export to local directory FOXML formatted data for ingest by Fedora Repository.
Let me know if these are of any interest to the PKP project