Everyone seems to be 'excited' about GTA 6. Fair play, I'm fine with people thinking up concepts and having ideas, but everyone seems to think it'll only be a few years down the line.
Some execs at R* said they're not working on GTA for the time being. Now V is released they want to think about some other games before they start on anything else GTA. GTA V was only being made possibly only months after GTA IV was even released so that means it was five years in the works. When R* say they're taking a breaking from GTA it means another 1-3 games can be coming out before they even think about VI. So let's assume it'll take about the same time to make as GTA V did. Assuming more games come out between, they could take about 2-3 years to make. Assuming they overlap, it could be at least 3-5 years before they GTA VI is introduced to the production board.
Then with GTA VI which of course "will have to top every GTA game to date" is going to take more than 6 years, which means it's going to be well over 2020 until we see anything about a new GTA VI game.