According to my first calculations for this thread: By the 4th week of last year, the PS4, Xbox One, and Nintendo Switch sold through roughly 7.15%, 4.97%, and 5.75% of their yearly sales respectively.
Applying those same percentages to this year, given the first 4 weeks of data we have now, this is what all three systems would sell in 2019:
PlayStation 4 - 14,644,360
Xbox One - 4,827,667
Nintendo Switch - 20,292,569
Thanks for this thread, I really look forward to seeing it updated every week.
I also like your post I quoted, hope you'll update the calculation every now and then !