Mario Kart has 30 million on lock.

Smash will continue selling until the Switch is dead so its pretty much guaranteed to hit it as well.

Zelda BotW is still THE killer "app" for the Switch and also will continue to put up good numbers until the Switch is out of stores, so I think it'll just barely creep over 30 million.

AC is a big question as we need to see how its legs are a year from now, two years from now, but I think it has a decent chance as gamers and casuals seem to buy it and love it in droves.

Mario Odyssey is dead even with Zelda now but has a bit smaller legs so I think it'll probably fall 2 or 3 million short. Pokemon had an insane holiday launch but fell off badly in its second quarter, I doubt it's legs will carry it another 13 million and assuming more critically acclaimed Pokemon comes out in a couple years I think that'll cut off any chance at 30 million and it'll fall several million short. The only possible future games I could see maybe hitting it are a brand new critically acclaimed 2D Mario game, a Wii Sports remake upgraded to perfection and sold at a budget price (probably won't happen tho), or if Game Freak blows the next Pokemon out of the water and totally revolutionizes the series so that it does even better than Sw/Sh (this is extremely unlikely tho).

So looks like I'm gonna say Switch will have four 30 million sellers when it's all said and done: MK8D, Smash, BotW, and AC.

Mario Kart
Animal Crossing
Breath of the Wild
Smash Ultimate

In that order, so 4.

I see Odyssey stalling at 25m and Sword and Sheild stalling at 22m.

Can't think of any other games that can even compete with these 6 outside BotW 2, Odyssey 2, or Gen 9 Pokémon, but even then all three of these games should make less than their predecessors, putting them below 30m.

I say 3 Mario Kart and Animal Crossing and Smash. I don't the Zelda will make it.
Funny note this thread is being there for more than 1 hour and there are no "no way", "what are you thinking" ... yet. People are now being very cautious around switch prediction lol

"Double post"

Id say 2 are certain:
Mario Kart 8 Deluxe
SSBU

Very likely:
Animal Crossing

Probable:
BOTW

I dont see any others making it

MK8DX and AC are guaranteed if you ask me.
I'm not a 100 % about Smash, but it certainly wouldn't suprise.
BotW on the other hand I think will fall a bit short maybe hitting around 27 mil, which is ofc still incredible.

Only MK8D. I’m not a believer yet that hardware sales won’t decline next year and these evergreen depends on high hardware sales to sell high numbers. I hope BOTW and smash does make it because they genuinely deserve it for being so good

Easily 6+

Certain:
Mk8d
Animal Crossing

Basically certain:
Smash

Highly probable:
Botw
Mario Odyssey
Next Pokemon

Possible:
Sword & shield

new 2d Mario

Unlikely:

Botw 2

Next 3d Mario

We'll have to take into account that the Switch itself will be a 100-150 mil seller and many of these games Will continue to sell for the whole of it's life. 

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.

I only think MK8D will make it. I don't think the other games will come close. Lets just wait and see when and if these titles pass 20 million first lol.