If BA continue the Almaty service then the only way to use the A321 would be via an intermediate stop. My guess (and it's only a guess) is they will continue it with the 767 or 777 which they used on that route prior to handing it over to BMed.
But I was curious to see that although BA have already placed their flight code on LHR-ALA they have not done so for the Almaty-Amritsar (ATQ) rotation.