Games are using many cores since years.... is that so? The truth of the matter is, very few games can use more than 4 threads. Tbe sweetspot for gaming now is 4c/8t. Very few games show improvements with more threads. Now, 3 hears from now... with you.
Earthdog is correct but I believe the timeline is even further out the 3 years.
The Q6600 & Phenom I came out around 2006-2007 (I'm too lazy to look up exact dates). It only took ten years for dual cores to go by the way of the Dodo for gaming PCs (and 2c/4t is still a viable option today). Way too many obstacles for the gaming industry to move that fast forward;
May 2017 is the first time in Steam's Hardware Survey that quad cores outpaced dual core CPUs (currently 59 to 36% in Sept 2017). Prior to May they were dead even. Six core + CPUs barely break 2%. That is a lot of new CPU hardware that the average PC gamer is not about to give up on.
Laptops still outsell desktops two to one and most laptops use dual cores CPUs or 2c/4t.
Improving CPU performance doesn't sell games. No one posts pictures of great looking AI on their web sites for games. Graphics sells games and graphic cards are much easier to upgrade for the average PC gamer.
The PS4 Pro and Xbox One X - (the former launched in late 2016 with the latter launching next month) both are re-using their jaguar CPU (glorified tablet CPU) just with an OC. The AAA titles are all driven by the consoles so they can't push CPU demands to current desktop performance levels with a CPU made for 2012 consoles. New consoles won't launch until holiday season of 2020 (maybe even 2021).
Unless 120 & 144hz monitors just take off as opposed to 2k monitors (or combined with), you are going to see a similar adoption rate of five years for the mainstream PC gamers to adopt six core CPUs and ten for quads to be avoided for new builds.