Well you could review this thread Can I use its 802.11ac AirPort Card on my RMBP 15 (mid2012)? As you can see there is a bit of debate on the subject ;-}
To start with the part is still not available and I don't think it will be for quite sometime as Apple will eating everyone that comes off the assembly line.
OK, So lets say you got one, the next issue is the antennas within your system will need to be the same as the newer models which just by looking at the tear downs I don't think they are. So that will crimp the throughput.
Next, Do you really need that kind of throughput? Most of us just don't have internet connections that could even push 1/2 as much down. Now, if you had your own server to access then you might but that also means your server is setup to offer out that much of a stream. Again, most of us just don't have RAIDED systems that could do this.
Don't get me wrong here. In the future we will likely have this level of throughput but thats still a good five years away. Bottom-line here save your money.