There's nothing that says an iTunes rewrite would necessitate opening X programs to sync content. It's trivial to envision an architecture where a sync service

There's nothing that says an iTunes rewrite would necessitate opening X programs to sync content. It's trivial to envision an architecture where a sync service is aware of and can pull from those X repositories. In fact, iTunes already works like that with regards to contact sync'ing (from Mail) and the optional iPhoto/Aperture photo sync'ing. And the only time someone need open those individual apps is when they want to consume or manage that content.