The 2060's performance is excellent at 1440P even with high/max detail in today's games. I suspect that if/when/by the time more VRAM is required for tomorrow's games, the card can only be utilized then for 1080P gaming, at which point 6 GB of VRAM would be enough...
If one truly believes 8 GB of VRAM will be an issue soon, get the 1070 Ti...; the performance differences between the two are about nil at running almost everything today anyway...