I for one certainly plan to stick around on VGChartz as long as the forum is online; I've been here ten years already. And I really don't think it'll take that long either, they'll probably sell 130 million in the first five years.
Not sure what parameters could really decide this within just the first year or two.
VGC has year end 2016 numbers for PS4 + XB1 as 53.5m+27.9m = 81.4m. That is 43% of the 190m total you suggested about 3 years after launch (including all holiday sales).
So, 43% of 130m is approximately 56m. I'll bet that combined sales of PS5 + Series X are 56m or less combined by year end 2023 (using VGC numbers). That should be enough time to tell which of our predictions was actually on the right track.