If we're talking lifetime sales projections then yeah anyone discounting 2D Mario is being silly, but I'm assuming whoever it is you're refering to are talking about the more immediate future. Nintendo already has a lot on their plate currently, though they could still have another big game announcement, but most probably expect/want that announcement to be Animal Crossing, I know I sure do!

It could potentially be a system seller, but only if they drop the New Super Mario Bros branding. That series has been stale ever since 2012, so releasing another one would do absolutely nothing. If they come up with a true 2D Mario successor that actually shakes things up, I could see it becoming a hit.

Also, not buying the idea that Mario Maker is a true replacement. There are a ton of people who would rather play an entire game of professionally made levels than the noobish quality that fills Mario Maker.

No, NSMBU would have done tons better it it wasn't released on the WiiU.

Of course SMB is a killer App.

I believe there's a 99,9% chance it will be released in 2019.

And yes, the NSMB series is worn-out, a new formula is needed.

edit: Another note to the OP.

I think SBM is a system seller, but not a good launch title. On launch people expect a game able to prove the potential of the console itself and so to justify its purchase.

SBM is a system seller for an established platform with an affordable price.

Just have a full campaign/story in the next Mario Maker job done. No sense in having both except cash money.

Nintendo will need to branch off 2D Mario into two sub-categories - the "Super Mario Bros" Nintendo-designed series, with more complex mechanics and a story, and player-designed Mario Maker.

I loved Mario Maker, but I still do enjoy following the story and having mechanics carrying from stage to stage. Nintendo COULD release both together in one package, but that's missing out on an opportunity to sell two separate units, and besides, it messes with the focus and could confuse some.

sigh, i just want the damn virtual console store.

I also want a 2d mario game, i really enjoyed them on the Wii. E3 its do or die for my game library, if nothing that interests me is announced, i will be better served trading in the switch, and waiting for a better version with VC or at least a new 2d mario.

I just want nintendo to let me throw money at them but they are not making it easy.

I live for 2D Mario! Switch needs to make this happen soon. I enjoyed the hell out of NSMB Wii and Wii U (Wii was better overall of the two). Adding 4 player coop was a fantastic game changer.

2D >>> 3D :P

I'd love to see a new kind of 2D Mario - something that doesn't follow the 'New' branding or aesthetics. There's no rush, really - if Smash, Pokemon and potentially Animal Crossing launch in the next 12 months (along with new IP like Labo), 2D Mario could be late 2019 and Mario Maker 2020.

But but but, dat fur!