Now for some better news: Grand Theft Auto VI is apparently in the works. This makes sense; GTA V was released in 2013, a full five years after GTA IV. It takes a serious time investment to build a game as huge as a main GTA title. GTA V was also launched on then-current consoles and re-released later as a port for next-gen consoles. Expect the new game to take full advantage of the aging, but still current, Xbox One and Playstation 4.
That being said, no hint of the location. If Tokyo was scouted years ago, maybe it'll be back in the running for GTA VI.