Mario Kart 8 Deluxe
Animal Crossing: New Horizons
Super Smash Bros Ultimate
I don't think BotW can do it, though I do expect 25M+ in the end.
Pokemon SwoSh will have their legs cut short by the next Iteration of the series. And I fear that's true for the next one too, so probably no Pokemon.
As for a potential 2D Mario, there are already 2 on the Switch (NSMBUD and SMM2) and only reach to 12M combined. I think the notion of these being 30M sellers come from the DS and Wii versions which both sold 30M - but also came after long years of only 3D jump'n runs on the market when many were waiting for a good 2D one. My stepfather for instance gifted me with both his N64 and PS2 because he simply couldn't find any good 2D jump'n runs (apart from Mischief Makers) on those consoles and rather tried to hook up my old NES to their TV to be able to play Super Mario Bros 1-3.
Long story short, the New Super Mario Bros came out after a long drought of classical 2D Jump'n run and thus everybody jumped at the occasion. But the situation is different these days and 2D Mario doesn't have that broad appeal anymore due to this. Case in point: The 3DS version NSMB2 only sold 13M copies. So no, 20M may well be possible, but I don't think 30M would be achievable with a new 2D Mario title.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454