That's an interesting use of IM, certainly, but I think it's tacking on functionality that doesn't belong.
Perhaps a different app that might follow the same conventions as IM, but not use IM applications? I can think of a dashboard-style app that would use Rendezvous to establish connections and do the actual transmission using Jabber or something like that.
Your notion of an all-in-one app runs counter to small pieces loosely joined and the general UNIX design philosophy. I'd like to see a number of different apps that can all interoperate or not, depending on your usage.