They're downplaying it at DC already, but why not. Superman should look beyond his borders - but how bad will they portray the tension of the regular public against him now?
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"I'm not smart so much as I am not dumb." - Harlan Ellison
well, he got honorary citizenship to who knows how many countries in superman 4.. i know, i know.. different canon.. point is he doesn't have to denounce his US citizenship to be honored as a "global citizen".. as a matter of fact, he can be NOT a citizen of any country and still be superman.. he shouldn't be limited just to the "american way".. superman is superman, may he be in the USA, the Philippines, Iran, Iraq, Kuwait, China, North Korea, South Africa, Apokalyps or anywhere.. but not on krypton.. he's just kal-el in krypton..
He's been operating outside the USA at various times over the years anyway, his base has just always been Metropolis. I really don't see this, even if they somehow went with it, changing the status quo.
He's always travelled round the world doing good deeds.
I think this makes perfect sense in that Superman should be a citizen of the world, not just one particular country. If anything, executing this idea would make him that much more of a universal character.