The extension would be to accomadate the A380's at the moment i dont think Manchester has any gate's or stands that will.
Apparently there are two stands - one each on T2 and T3 - that can currently physically accommodate an A380, but passenger access would have to be by the lower deck only. Not ideal, to say the least.
Of course, there's bags of apron space to park an A380 remotely, but the same passenger-loading issues would exist - compounded by the need to bus the passengers out to the aircraft.