So, it sold over 2M WW in Oct. Let's say that's 2.2M. I believe I read it sold ~1M in Nov in the US. That's 3.2M. It hasn't even hit 1M in Japan, yet. For Nov (this includes one day of Oct and 3 days of Dec) it sold ~392K. Let's be optimistic and say it sells ~2M for those two regions for Dec. That still only brings us to 5.6M for what will be, by far, its two largest regions. Not seeing where these extra sales are coming from. Sure, you still have Nov and Dec in the other regions, but Nintendo isn't the force it is in the US and Japan there. So, I could maybe see another 1.5M for them, bringing us to 7.1M. And Nintendo's digital sales ratio is nowhere near what it is on the PS4 and XBO. So, at best that would get us to 8M-8.5M.
Again, these are best case scenerios. Over 2M could be 2.01M. Mario may only sell 1M-1.5M during Dec in the US and Japan. It may only pull in 1M from the other regions. It may only see 5% of its sales through digital. I think 8.5M will be the ceiling. Still, ~5.5M is a nice floor to have.