The last three generations, combined sales for Microsoft's platform and Sony's platform have been remarkably consistent. PS2X managed ~182 million. PS360 managed ~173 million. PS4XO are currently on ~162 million, with another decent-ish holiday and a final year of trickle sales to bring it between those previous totals.
It's an interesting pattern; it starts to look like there's a ceiling of 185-ish million for what you might crudely term the hardcore console market, and that the combined total will always finish within touching distance of said ceiling.
In the XSX/S prediction thread I went with a prediction of 68 million for the XSX/S. If the pattern holds and my prediction for XSX/S is in the right ballpark, then PS5 should finish in the range of 107-117 million. That's slightly less than what the PS4 will finish on, which seems reasonable given I expect XSX/S to put up a better fight against the PS5 than the XOne managed against the PS4 (but still way off parity).
I'll cast my vote in the 110-120 box.