I had one Mk XII green console drop in an a B'tran mission once. The problem is that Uncommon Mk XII gear has the same stats as blue rare Mk XI consoles of the same type. Other than for status or something, having mk XII consoles right now is pointless.
Crafting blue consoles does just as well, so I don't see the point in getting them at present. I'm semi surprised that mk XII purple consoles aren't a part of STF turn in rewards for chips or Proto Salvage. This give many players don't have anything to spend Proto gear on now.
And I fear to tread a tic, what will happen when Mk XIII and Mk XIV gear appears, without some foresight on the devs part here. Course nothing is perfect anyway, so worrying again isn't worth it, with gear.