Chosen Solution
The Apple developers forum confirms that the new Auto Unlock with Apple Watch feature offered in MacOS Sierra works only with an 802.11ac, not with an 802.11n. So if you want this feature to work, you will have to replace your <2012 n with an ac board. The question then is the part number that corresponds to the 802.11ac that works in a <2012 MBM. Update (01/22/2017) Yes. Mac Mini.( And some more characters to meet the minimum requirement.)
Sadly the Airport boards are very different between the 2012 and 2014 models:
2012 board
2014 board There is no upgrade option available. For a short time Broadcom offered some engineering samples which some people were able to get (long since gone). Broadcom never offered a production part as Apple went with the mini-PCI interface board in the 2014 model.
