Do you expect MK9 to release in the next few years? A 2022 release for MK9, that coincides with the rumored 4K Switch, would kill off MK8 legs. I also find it hard to believe that MK8 will have similar legs in 2021 that it did in 2020. Wasn't it selling millions of units a quarter, in non holiday quarters too, during 2020? I don't think that's sustainable.
As for Spiderman, we know its over 20+ Million, and if that was the figure before the holidays, it could be around 21 Million at the start of 2021. Needing to sell 4 - 5 Million in the next couple of years, entering its third year on the market with numerous sales and DLC, gives it a good shot. PS4 hardware is finished selling but the PS4 userbase is still active. TLOU2 and GoT won't stop selling in 2021 either. During this November, Spiderman placed 11th in the PSN PS4 charts while Miles Morales ended up at 3rd. The game still has a bit of mileage left.
I don't think MK 9 will release on switch. I can see it being a launch title for the proper successor. It doesnt need to sell at the same level as 2020 to reach 40 million. It has consistently been selling very well since it launched. I dont see why it'll suddenly just stop after this year. Mario kart is one of those games that will just keep selling as long as consoles are being sold.
The ps5 and remaster are going to kill its legs. It might get another 4-5 million but it will be very tough. There is just a lot going against it.