To declare him an Antipope would undermine many of the cardinals, since many of them owe their positions in the CC to him. And there is the further complication, that they would need to decide whether he was always an Antipope. If he was formerly a legitimate Pope - when did he forfeit the Papacy ? And how ?
Do you see a solution ? I don't. I think he will just have to be tolerated until he dies or abdicates. A lot of what he does was prepared for by JP2, with his "Ecumenical Martyrology", and similar undertakings. In the meantime, the Popes will have full freedom to corrupt the Church. Which they are v. good at doing.