Ok so this is what i heard, and i might get in trouble, but i dont care. TFS always seems to be withheld the good gossip, so here it is (no idea how truthful, but the person who told me works as a PA to one of the major Photographers );
So it doesn't seem to be about KK (i think), however it was a huge blow out between Sozzani & Meisel! She wanted him to exclusively shoot the China story only for VI cover ed, however he agreed to shoot Fei Fei for Wintour's May issue. And Franca really resented the fact he chose them over VI, after years of loyalty she has showed him. And despite of Meisel having a very bad relationship with Anna, especially in last few years, Sozzani always had his back. But when he picked US Vogue over VI, she decided its time to use someone else to shoot the China cover story.
It's most certainly an end of an era, so unless they have KK in super Chinese look on the cover, its the matter of personal resentment, and perceived betrayal which led Sozzani to go with someone else for the cover.