You mean like when gamers didn't need the 4GB of the 290X and the GTX780's 3GB was more than enough, or when gamers didn't need the 3GB of the HD7970 and the GTX680's 2GB was enough?
For reference in both those examples the cards with more VRAM lasted their owners longer.
And now 6gb is borderline. So soon the 1060s will be crippled or stuck in low detail settings while 8gb 480/580/590s cruise on.
I'm betting Doom Eternal will eat more than 6, seeing as the 2016 one wanted 5 for highest texture settings. In which case bad times for anyone who ordered a 2060.