Media event set for September 9, launch likely ~10 days later.
Photos of Likely 802.11ac 'Gigabit Wi-Fi' Card From Next-Generation iMac Surface
While the reports suggest that the new card is intended for the next-generation MacBook Pro or MacBook Air models rumored for launch at next month's Worldwide Developers Conference (WWDC), a commenter on the Tonymacx86 discussion thread points out that the card is actually nearly identical in size, shape, and layout to the Wi-Fi/Bluetooth card found in the current iMac.
The BCM94360CD card, which is very likely a custom design for Apple, contains Broadcom's BCM4360 802.11ac transceiver chip, offering support for the in-process Wi-Fi standard that allows for triple the speeds of the current 802.11n standard. An apparent date code of "1240" on the part suggests that it was manufactured in early October 2012, several months before Apple was reported to have struck a deal with Broadcom to bring 802.11ac support to its 2013 Macs.