on macOS Sierra GM and Xcode 8 GM, I launch Xcode after doing the install over the latest beta, get the Installing Components dialog and press Install, but it never completes.
Well, the progress bar is filled out, but the window doesn't go away.
Just tried Xcode-beta 6, same issue.
Filed as radar 28211205.
This has basically bricked this laptop for development, since I can't use Xcode (neither the GM or the previous beta).