Alright, by the morning the MAS had updated Xcode - now it has 6.4, 7.0.1 and 7.1 available for swift projects.

I updated the Mac, and got the server back up and running but not on 7.1 yet. So moving to monitoring but not fully fixed.

Installing Xcode 7.1 for Swift 2.1 support, and daring to hit the "update button" for the OS install. Don't expect this to be a long one.