I had a feeling Isshu was going to be based off of New York. With the confirmation of it being based on New York, at least the debate between the two regions New York and Shanghai can come to a halt.
Being born in New York, I can't say I'm disappointed; although that's a bit bias of me to say. :( Still, while both Shanghai and New York had a lot of heavy evidence that could have proven each region to be true, I feel as though New York just had the extra influence. Liberty Ticket being one of the most major to follow up with the Statue of Liberty.
Also, even if it were to be based upon one city alone, that doesn't necessarily mean you have to take it as a bad decision on GameFreak. For one, it's Pokémon, so whatever New York has, they can take that and expand the idea; for example, the desert above Hiun City. While it's confirmed to be based on New York though, I have a thought in my mind that the developers took some influence off of Shanghai as well.