If I'm right about Izanagi being a Time effect, and also if Zetsu did in fact eat Itachi's body as he did for every other dead Akatsuki member, then there is absolutely no chance on Itachi physically coming back from the dead. Only through soul imprint style thingies can he return, but that's only partially. Face it, we'll never, ever, ever see Itachi's true power. Which is actually better, because at least then Kishi can't fail to live up to our expectations, and we can all keep on dreaming.
Zetsu clearly didn't eat Itachi. There was never stated such a thing, we don't even know where his body is atm.
Soul imprint is a probable idea, but I suppose it will be nothing like Minato, more like Madara who is a shadow of himself.
We know that it's possible for one to return in soul-form into the physical realm, since Madara needed Nagato to cure his
body.
We actually never saw him being serious on anybody before, he wasn't even serious on Orochimaru. Madara said it, heck everyone said it.
And to the expectations: How long was it since Itachi died? Kishi's still hyping him to the max. Nobody else got that hype before..
Seriously, the only thing I wanna see from this manga is Itachi fighting with his true potential, not how he fought against Sasuke.