So, for an aggregator to be really useful to me, it needs to de-couple the aggregation/datastore from the presentation. When I'm at work (or not at my home computer in general), I want to be able to get at the data via a web browser. When I'm at home, I want a nice, powerful UI like Harvester or Syndirella or NewsGator. When I'm travelling or on the train or whatever, I want to be able to read on my PocketPC. And, most importantly, I want all of these to use the same data set. When I've already read something at work, I want to know that when I get home, and vice versa.
I think I will work on such a WS anyway. It can be useful by itself, and could even more give ideas to others.
Hint for the creators of SharpReader, RSS Bandit, Harvester and others: please create add-in support in your RSS client readers. Soon (and I first) we will need to integrate into your software. Feeds or feed lists may not always come from simple HTTP GET but from web services for example.