Answer to "Can I use its 802.11ac AirPort Card on my RMBP 15 (mid2012)?"Hi, Everyone. ^^ As you know, RMBP 15" Mid 2012 had installed Airport card, BCM94331CSAX (Support 802.11a/b/g/n) RMBP 15" Late 2013 has installed Airport card, BCM94360CSAX (Support 802.11a/b/g/n/ac) BCM94360CSAX has same demensions(? looks same), 3-antenna ports, and interface connection between BCM94331CSAX. I just installed BCM94360CSAX in RMBP 15" Mid 2012 basic model, last weekends. Wi-Fi Link speed is 1Gbit/s with ac mode, right now. (450Mbit/s with n mode, past) It works very well and still using AC mode without problems. As a results, RMBP 15" Late 2013's 802.11ac airport card is compatible with RMBP 15" Mid 2012. But, I don't know there are any technical issues.
Answer to "802.11ac Wi-Fi card fits 2012 model"The new Airport card (802.11ac Wi-Fi) in MacBook Pro 15" Retina Late 2013 is compatible with MacBook Pro 15" Retina Mid 2012. You can look at under site. http://cafe.naver.com/inmacbook/916510