Getting back to the brainstorming, something I'm fascinated by is the potential for follow-ups to Mario Odyssey and Breath of the Wild. Really for both franchises I'd like to see them lean more towards the direction of the other one. For Mario I'd love to see something that's TRULY open world but still has the exact flawless mechanics and pick up and play style of Odyssey. Imagine being able to explore all the kingdoms without having to switch between them on the map. The game could be a bit smaller scale than Odyssey but still employing a massive world with different environments to explore.
I'd really like to see Zelda get a more linear game set in the world and lore of Breath of the Wild. As a couple others have stated, Breath of the Wild is a punishing experience and not the most pick-up-and-play friendly. I think a mechanic similar to Majora's Mask could work wonders for Breath of the Wild's overworld...where the challenge isn't about the endless exploration but moreso how much you can accomplish in the massive world over a set period of time with different tiers of goals that gradually get more difficult. This would still give you the feeling of progression but make the huge world a little bit more easy to handle with more straightforward goals to accomplish.
While were on the subject of follow-ups...while I think it's less likely to see a Mario Kart 9, if we do get one on the Switch I think it absolutely NEEDS to break the game completely and create a Diddy Kong Racing style open world hub. How cool would it be to drive your cart around a HUGE Mushroom Kingdom setting that branches out into different tracks and cups. You could still have the same mix of new tracks and classic tracks, but the open world setting would add another dimension that we simply haven't gotten yet with Mario Kart. An adventure mode would be the icing on the cake. While were at it, let's get a current gen Diddy Kong Racing as well, please!
Something I heard discussed on a podcast that I'd love would be a Gameboy Classics Collection...Imagine Pokemon Red/Blue, Metroid 2, Super Mario Land, Mario Land 2, Wario Land, Dr. Mario, Tetris, Pokemon Pinball, the Donkey Kong Land trilogy, and the original Shantae all on one cartridge. Save the home stuff for Classic Editions, but the Switch would be a perfect fit for a Gameboy anthology.