One of the Dungeons and Dragons artists got in trouble for creating an amazing drawing of a giant then using Stable Diffusion to make it really pop. A different Ilya than the one we all know and love got in a bit of hot water [0].
AFAIK, MtG art is all gig work. Art is part of the product and to the extent that AI gets involved it would be about elevating the value rather than cutting costs.