I don't see a need for 802.11ac while I'm out and about. At home I'll use it for fast transfer of big video files between my computers. I plan to add it to my rMBP with an adapter attached to my USB3.0 hub. That will allow me to ditch the wired Ethernet connection and the nasty Thunderbolt-1GbitEthernet adapter. So, just one cable from my rMBP to the hub and I'm done.
Yeah, it would be cool to swap the internal WiFi card, but that will probably be more expensive, and it may not even be possible. We'll have to wait and see.