On OpenGL, the little camera in XCode (iOS) is enabled. For Metal, it is not. Did this feature not make the first seed or am I missing something I should know to get a GPU frame capture?
Where is the GPU Frame Capture I keep seeing in WWDC Videos?
AHA! Edit the scheme per https://developer.apple.com/library/prerelease/ios/documentation/Miscellaneous/Conceptual/MetalProgrammingGuide/Dev-Technique/Dev-Technique.html and set GPU Frame Capture to Metal. Looks like "Automatic" doesn't work at the moment (or at least doesn't do what it would imply).
Note: I hit this when running a SpriteKit project, so it may not be a problem for those using Metal directly.