I don't have the source anymore, I think it was in Michael Rosenbaum's podcast, but Gunn had said something to the effect that he'd like to approach the DC Universe in the same way as Tolkien's Middle-earth, implying (at least this was my understanding) that places like Gotham, Themiscira and therefore Metropolis are indeed fictional places, with their own characteristics and would be treated as such in the DCU.
Based on this statement, I had indeed expected this Superman movie to attempt to embrace an aesthetic "outside of time and our reality" for something more singular. The image revealing the costume had tempered this hypothesis, but all these new photos today finally seem to be going in that direction.
Pretty cool!