well historically Nintendo typically makes money from hardware/accessories so thats something that they would be losing out on by going 3rd party as well as losing royalties/paying royalties.

One of the bigger reasons I think this would happen is because Nintendo probably wants to get the most bang for their buck considering all the time, energy, manpower and resources that went into the BotW engine.  Considering the frugal nature of Nintendo, I wouldn't be surprised if they milked the engine like Bethesda did with the Gamebryo engine.  I especially would like to see a large-scale Metroid game done utilizing this engine.

Real 3D Mario
Pokemon like RPG
Real Paper Mario
Luigi's Mansion 2

Tales of game
Mario Soccer game from Next Level Games
Would also love a Kirby's Air Ride sequel

Do another Orre style Pokemon game with a 30ish hr rpg plus multiplayer for the handheld games
New F-zero (I shouldn't have to say this)
New Custom Robo. I know Smash is the cash cow but this series never got much love
Fire Emblem fighting game from arcsys

p.s. no more censorship

Mature games for mature gamers such as myself. Brown boring shooters with big cinematic influence. Racing games in 30 fps. Immersive interactive novels with Hollywood cast. Day one 30 Gb patches. Laggy paid online. Games for which 90 % of budget spends on marketing.

I think it would be awesome if they resurrected some existing (but dormant) IP like Wave Race, Excitebike, Startropics, Advance Wars, Golden Sun, etc. Reboot some classic franchises like they did with Kid Icarus: Uprising and Donkey Kong Country Returns? Maybe even buy the rights to some classic IP from other developers like Crystalis and Faxanadu and inject some HD polish into them?

I can't really say it any better than Veknoid and others already did. Variety and a steady stream of games is all I want. And perhaps a 2D Metroid reboot in the vein of Zero Mission.

Awesome question!

More ambitious games.

Is this a trick question?

A 2D Mario platformer akin to the ones from 25 years ago. No 3D inclusion, no gimmicks, no motion controller things, no Amiibo. Just a 2D Mario with the stuff that made SMW special. That's it. I know Super Mario Maker is there for that, but it's not enough.