User blog comment:Insistente/Ichigo also survived Auswählen like Uryu/@comment-10961564-20130730184931/@comment-11051098-20130731080219

I don't think that's the reason. Yhwach said that Uryû was the only Gemischt who survived the Auswählen, and Ichigo's Quincy powers were yet not awaken at the time. I rather think it has something to do with Ichigo being part Shinigami and part Quincy.

Maybe he surpasses the limits of a Quincy because he's a Shinigami/Quincy, like he apparently surpassed the limits of a Shinigami because he's a Shinigami with an inner Hollow, and possessed Hollow powers like Cero and Sonído when he was in a full Hollow form. And maybe that's why he's considered a Special War Power.

After all, now that he has his true power and an Asauchi-based Zangetsu, he should be one of the strongest Shinigami, if not THE strongest, in terms of pure power, despite his origins being a human born to a Shinigami dad and Quincy mom.