I’m interested to see how developer support for Mac App Store-only features plays out.
Two big ones: iCloud document storage and Notification Center. Both of these are slated only for third-party apps from the Mac App Store.
Many developers, though, have been maintaining non-Mac App Store versions of their apps. If this continues, such apps are going to lose feature parity between the App Store and non-App Store versions.
Apple is not taking the Mac in iOS’s “all apps must come through the App Store” direction, but they’re certainly encouraging developers to go Mac App Store-only with iCloud features that are only available to Mac App Store apps (and, thus, which have gone through the App Store approval process).
This is, along with misconceptions of Gatekeeper, my worst fear regarding the future of the OS X platform…