Also, because his characterization was sacrificed for Kabuto's, his sudden decision to just be a spectator and even help Konoha is just odd and barely plausible. Whereas if he'd been izanami'd by Itachi (I don't get why people above think that's impossible; in this scenario, he would have gone through the same ANBU identity confusion as Kabuto, and hence would not know his true self), it would have been smoother.
Who cares about HOW the hokages would have come in... when has plot ever stopped Kishi? He would find a way. Maybe Sasuke would have asked Itachi if there was a way to speak to them, and Itachi'd be like,
"Sure come with me, I still have 10 minutes before the jutsu fades. Let me just stab my paper stomach while wearing this mask and oh--Here they are. K bye guys. Oh hey Third. See you later in Hell

"
EDIT: or you know, whatever. Plot is like putty to Kishi.