I too would welcome if iTunes could return to be a music player. It must be a huge pain even for Apple to work on such beastly monolithic app that does almost everything except the laundry.
- iPod/iOS sync
- iTunes Store
Break the primary route to a user's wallet/content, and the Apple experience starts to fall apart.
The hard bit is in the overall experience. Splitting one app into 5 or 6 was manageable on iOS but could be unwieldy on OSX.
Think of how terrible it would be for your Apple TV to then break out and have to look at multiple applications for your content instead of one.
I highly doubt apple would make the mistake of creating more mini apps to manage each of the various items; just would be a stupid design move.
For all we know, iTunes could be (and probably is) a fully modularised code base, with minimal cross module dependencies. The fact that we see it as one application tells us nothing about the underlying code.
Even the UI parts for different functionalities can be neatly modularized in different IB files, the only thing they all have to share is the main menu.