This thread's poll is only about Mario Kart 8 Deluxe's sales, so the Wii U version of Mario Kart 8 is not included in the figures. If you want to predict a total for both versions combined, you have no choice but to post in this thread.
Mario Kart 8 Deluxe shipped 24.77m units by March 31st 2020. What are your lifetime sales expectations?
Here is its shipment progression. Current quarter followed by LTD.
June 2017: 3.54m/3.54m
September 2017: 0.88m/4.42m
December 2017: 2.91m/7.33m
March 2018: 1.89m/9.22m
June 2018: 1.13m/10.35m
September 2018: 1.36m/11.71m
December 2018: 3.31m/15.02m
March 2019: 1.67m/16.69m
June 2019: 1.20m/17.89m
September 2019: 1.12m/19.01m
December 2019: 3.95m/22.96m
March 2020: 1.81m/24.77m
...
Bonus question: A common opinion is that Nintendo won't release Mario Kart 9 for Switch because Mario Kart 8 Deluxe is selling well enough to last the console's entire life. However, the release of a new game would be talked about a lot and therefore benefit Switch hardware sales in the long run without a doubt, and the game could eventually release as an early Switch successor game as Deluxe version with all DLC included and perhaps a few new features added, because that's already a proven strategy. In short, which side are you on: Do you expect to see Mario Kart 9 on Switch or not?
Legend11 correctly predicted that GTA IV (360+PS3) would outsell SSBB. I was wrong.
A Biased Review Reloaded / Open Your Eyes / Switch Shipments