[EGreg]

How will this affect TestFlight and other such apps? Don't they still need your UDID?

[perkof]

I beleive testflight doesn't use the App Store to deliver the application so should be okay.

An update to the testflight sdk should be sufficient for production applications with testflight integration.

[Aqua_Geek]

TestFlight gets your UUID by having you enroll your device in their MDM system. Support for this will likely never go away.

[JimDabell]

They use the UDID when the application runs to associate particular sessions with particular users, which can be extremely valuable for debugging purposes.