I agree that that Superman isn't the same one from KC.

The "S" shield is used when people showa future Superman, as is the grey temples. Even Batman Beyond used the "S" from the KC Superman (They did change the color from red to white though) so I think it's just excepted that an older Superman with less hope or what not will don that "S".

I personally think that this future Superman is referring to whatever is going to happen in Superman/Batman, with the whole Krytonite Meteor storyline.

I don't think another Crisis is needed. All that is needed is a DCU Bible. Something that tells writers what's what, and strong editors who do their jobs keeping Continuity flowing right. therwise Barry's sacrifice was meaningless.