Hidden Wi-Fi ac support
I think the MacBook Pro Retina Early 2013 secretly supports the Wi-Fi ac:
With the application WiFi Explorer, we see that it recognizes the ac network of my AirPort Time Capsule, plus, it's able to see the signal strength (which is different from the a/b/g/n network because of the beamforming).
More: The network in bold is the one currently used...
I think maybe Apple will release a "ac activator, like they did for some Intel Macs.
But first, we need to be sure that it's not just the app that recognizes the network.
So I need some testers to see if with (any another Mac and an ac AirPort Extreme) you can see the ac network and the signal strengh. The app that I used is named WiFi Explorer and is available here.
Note: My MacBook Pro Retina 15" is running on OS X Mavericks.