The biggest issue is that due to the Island system for containing the game world, any future GTA city would have to be a coastal city, at which point you're struggling to find any culturally relevant ones
Nobody cares about San Francisco or Seattle so you're totally wiped out on the West Coast though having a GTA in the Pacific Northwest sounds very exciting specifically being able to race around Puget Sound and the Olympic peninsula.
On the Gulf Coast outside of Florida you have Houston, New Orleans, Mobile and Space X
Houston is a soulless shithole where all the crime is petty bullshit as it doesn't even have gangs since all the native Houston gangs literally got genocided by the Feral Africanized New Orleans gangs after Katrina, which then proceeded to nigga moment themselves to extinction.
New Orleans is a completely worthless city in the modern era
Mobile is an irrelevant ghetto shithole.
Now you have the East Coast, between the Florida stateline and the Potomac all the major cities are located inland.
Your options left besides Miami and NYC is DC-Balitmore, or Boston
Then on the Great Lakes all you have is Detroit, Chicago, Milwaukee, Toledo and Cleveland