The AirStation WZR-D1800H was announced earlier this year, with Buffalo promising the arrival of this next-generation router by the summer. Just last month, however, Netgear said it would ship its own 802.11ac router, the R6300, in May. It's still may, so Netgear hasn't missed its date yet, but Buffalo must have hustled to beat Netgear to the punch.
To be clear, however, the 802.11ac standard has not been ratified by the IEEE yet. That isn't expected until early next year, and those who remember the long road to 802.11n ratification might recall that some of the early, pre-standard routers could NOT be upgraded to meet the final standard.
There are some early adopters who will probably through caution to the wind though. 802.11ac technology promises over 1Gbps transmission speeds. That is, of course, optimal performance; Buffalo's prototype router shown at CES was "only" hitting 803 Mbps. Theoretically, the standard can support up to 1.3Gbps.
Notably, there are no devices that can use the ac technology in Buffalo's products anyway. So, although the router is capable of it, your devices (smartphones, tablets, notebooks) aren't.
However, you could use the router and media bridge together, then wire-connect devices to the media bridge, which has four LAN ports. Wirelessly, once adapters ship with the standard, and assuming the standard does not change, Buffalo's router and media bridge (and Netgear's) will be ready.
802.11ac transmits over the 5Ghz band. It uses beam-forming to increase speed and range. It will, of course, support the 802.11n standard for backward compatibility.