without spoiler tags I'll say how would it be possible...
Ichigo has super reiatsu, that is bigger than any other shinigami (including any capitan I think) so he can much up with hybrids when they come (he never was gaining it, he just was aknowleading that he still can use more)
and if he hadn't be a hybrid since childhood he couldn't maintain all of it...
and if he needed to retake his shinigami power's than he probably needed to retake his hollow's powers as well... I think Ichigo is a perfet hybrid that just need to know how to control himself...
I think that Urahara created Ichigo somehow, and only unspoilerish prof is that Urahara knows that Ichigo can still grow and belives in him so much
