Chosen Solution
I was wondering if it would be possible to upgrade the WiFi/Bluetooth card in the Mid-2011 Macbook Air with the latest 802.11ac/Bluetooth 4.0 version?
It depends on what you are looking for here. If you want handoff services then yes, if you are expecting a faster WiFi the answer is no as your system only has one antenna. Review this site for the details on handoff: Continuity Activation Tool
