I put 96-110 million.
Let's say 2019 - 2021 are its peak years and it does a bit under 60 million during those years. That'll put it at 85 million or so at end of 2021. Depends on when it is replaced, but if it isn't replaced until 2023 then it'll probably be around 100 million when the next Nintendo system comes out. My best guess would be 100 - 120 million but i think beating the Wii by just a few million is more likely than beating Wii by like 15 million so I put 96-110.