iTunes already wants to be too much. It has a store (with credit card management), your local music library, a social network, movies that you are supposed to watch via Apple TV, podcast management, the app store, low-level device management, a set of ratings systems for apps and music and movies... It's too much in one package. It violates a lot of good design principles. For example, because it's got so much going on, they can't optimize it for any one task. A lot of people think it needs some decoupling, not extra features.
I think if Apple wants FaceTime to be on Windows and non-iOS phones, they need to promote the protocol and not just one application of that protocol.
* FaceTime on iTunes, for Mac and Windows
* App Store for OSX