This example is intentionally simplified to show that XMPP already solved that problem, and something you can run from the command line to see what the timeline looks like (and no, you won’t be receiving any IMs, only status updates).

A real implementation would look different, for one you’ll want to run an XMPP server not multiple client threads polling for each user, but the concepts are all the same: use XMPP to decentralize and exchange statuses.

This type of distributed system makes a lot of sense… But the largest problem that I see is that people already have a GUI IM client that they can use. So, what would the client for this really be? Another GUI IM(-lite) client? Would it be a web-based tracker (with the server tracking each person’s roster)?

I think it doesn’t quite live up to the ease of using Twitter, namely the lack of anything to install.

Now, I could see a web app that you gave your IM credentials to, and it tracked the people that you follow. You could then update your status there as well. But what you don’t necessarily want to (or expect to) receive IMs from everyone that you are tracking.