Blu ray? Social networking? Jesus lets brainstorm and think about what can we do to make that turd even more bloated.
There's bloat that slows down an application, and there are features that are lightweight and only run when you tell them to run. For instance the BluRay support will surely be part of Quicktime X, that iTunes will call as necessary. Hopefully FrontRow will also gain support (notice how FrontRow wasn't updated much with Snow Leopard - possibly it will gain a proper update tomorrow as well).
An iTunes written in Cocoa, using Snow Leopard's APIs, will feel very snappy and responsive, even as the features add up. It already incorporates webkit, so adding social networking ajax calls into the application might not be such an overhead as you expect.