Turkey, Russia. Australia or England.
Vice City? It's a depressing boring city that won't be the same without '80s setting.
America again? America isn't the only place on this planet, Rockstar, and with every GTA game and many Non-GTA games choosing the country as their/its setting, the location gets stale. Their is only so many times a person can play games with such location before they all start to feel the same. How is San Fierro going to feel different from Watch Dogs 2s or Driver SF's San Francisco?
You've proven to us that you're able to create a setting outside of the U.S. with 1998's GTA London 1961 and 1969 "Mission Paks" and given recent world events, the above countries would be perfect choices to do something a bit different.