“The example he [Dave Winer] used was wanting to un-follow a particular user for a day, then re-follow them automatically. It’s certainly possible to build this sort of functionality into an existing Twitter client, but I’d like to suggest something easier than herding all of the Twitter client authors in this direction. Specifically, rather than having the scripting support built into a Twitter client, why not just ask Twitter client authors to allow their clients to be pointed at alternate hosts that implement the Twitter APIs besides Twitter’s own servers?”
Umm…. because that would be a massive, gaping security hole?
Seriously, just because Dave thinks some kind of federated Twitter is the solution to his problem* doesn’t mean that opening up Twitter clients to evil hackery is a good idea. There already is an open source Twitter clone, in the shape of the excellent Identi.ca.
(* Dave’s issues with Twitter only appeared to start when they introduced the suggested user list and he wasn’t on it, leading to him not getting millions of followers who would have been baffled by his tweets.)