Interestingly, Apple has already started randomizing MAC addresses [1] on iOS (8?) and newer devices. Though maybe not quite as successfully as it seemed at first.
I believe this only works for broadcast packets. When you've chosen to connect to a wifi network, then your real mac address gets used. It would be a nightmare for shops that use mac filtering and other tools that expect standard mac behavior if the mac was randomized all the time. What Apple is doing is stopping broadcast packets being a unique value to track on.
[1] http://www.imore.com/closer-look-ios-8s-mac-randomization