TC, just because we dislike this particular idea doesn't mean we are against all and any changes. Anyway, it's a gimmick that has already been made in other similar franchises (Digimon and Dragon Quest, for example).
Well technically they already did this. B2W2 you fused Kyurem with the respective dragon to form black/white Kyurem. It was only for those pokes, but to say they haven't done it at all would be incorrect.