So I did what many suggested and kept TestFlight SDK in the release build to be prepared when FlightPath finally launches.
However: After following TestFlight's instructions for the predecessor called "TestFlight Live", TestFlight refuses to accept my App Store IPA (continue reading) and gives this message:
Invalid IPA: The keychain-access-group in the embedded.mobileprovision and your binary don't match.
I did what they said:
1) Made a release build and submitted to the App Store, with TestFlight SDK and checkpoint calls included, but -setDeviceIdentifier: call removed.
2) From Xcode Organizer window: Selected the submitted archive, clicked "Distribute" to re-structure it as a TestFlight-compatible binary, signed for AdHoc distribution over TestFlight.
Apparently this binary is garbage for TestFlight which lefts me wondering: How am I supposed to ever get to the analytics data once FlightPath arrives? Am I better off rejecting my submission and stripping out all the useless TestFlight SDK code or can this be fixed?