You can already do some of those things in a 3rd party app via API (except for in-app purchases and iTunes authentication). Of course there are downsides like the AppleScript API kind of sucks and you need iTunes app running for it to work.
However to really become a platform iTunes needs to move to the cloud. Let's hope Apple will get it right with their rumored iTunes streaming service.
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You can already do some of those things in a 3rd party app via API (except for in-app purchases and iTunes authentication). Of course there are downsides like the AppleScript API kind of sucks and you need iTunes app running for it to work.
However to really become a platform iTunes needs to move to the cloud. Let's hope Apple will get it right with their rumored iTunes streaming service.
Is there a reason to not use the Apple COM SDK for iTunes? link: http://developer.apple.com/sdk/itunesvisualsdk.html Or are we (you) talking about something more app store oriented?
That's just for writing visualizers.