Not a barrier, but yes, supplying melamine free (and what else creative Chinese factories might want to add) IF might be in some other markets not such a strong distinguishing criteria :):
Still - it is A2 and it takes probably a decade or so for other markets and competitors to build up their own A2 herds in sufficient numbers.
But yes - at some stage I'd expect all cows will be A2 and the advantage will be gone.