User blog comment:Noyas/Some questions about bleach./@comment-452405-20100425014407

I think children can be born in Soul Society, well that's what is said on Soul Society's article I think.

And all those guys you listed off for potential captain candidates, none of them can except Renji and Ikkaku (only if they learn of his bankai as well). Ichigo is still a living human and the Vizards, Urahara and Yoruichi have all been banished from Soul Society. Isshin too has his own life in the human world as he gave up being a shinigami, only regaining his abilities to deal with Aizen and the Arrancar.