They need to do something from the East, preferably Tokyo or Hong Kong. (I have lived in both of them)
Yakuza has always been in
Tokyo and Sega has much better knowledge of the Japanese gang and city culture - which is very important for a real world sand box game like this to make it feel authentic.
As for
Hong Kong, Activision is having the next True Crime set there developed by United Front Games (Mod Nation Racers), but that doesn't look too hot from the preview (but I am still intrigue to play the game because of the city). A lot of problem has to do with a Western developer lacking knowledge of that city so everything feels stereotype and cheesy.
In the end, I think the reason why Rockstar avoid doing cities outside of America mostly has to do with their lack of knowledge and the fear that they are incapable of recreating them in an authentic way.