Steve Palmer seems to be the leader/lead developer for Vienna 2, an open source RSS aggregator, for OS X, with the spit and polish of NetNewsWire. Given MacOS's inherent scriptability, this could be a good platform to work on exploring a hyper-extensible desktop aggregator. Hey, Brent Simmons is a great guy, and there are other extensible aggregators out there, read Awasu, but occassionally you just don't want to wait for the main developers.