I personally love 3D as well (shout out to Mario 3D Land for making me fall in love with its potential!). I hope it can return somehow. I was thinking of a home console too and didn't even consider portability. But since Nintendo merged home and portable play, my idea would have to include that too. Maybe it could be a device that docks to the home TV again, but this time with a graphical upgrade? There could be home console exclusive games if they don't play well in portable mode, and portable exclusive games if they rely on a touchscreen maybe.
Dreaming super big, maybe in the future internet connectivity will be so advanced that devices are no longer needed and everything is just streamed to any screen you possibly own (or your high-tech glasses that replaced your smartphone? 8) ). However, I think we are still far from that, probably 25-40 years away from a playable state of streaming. It almost feels dystopian thinking about it, actually. :o
I agree that any improved online functionalities on Nintendo systems would be nice!! They could have their own voice chat system and also support Discord, like other systems. I like the idea of them creating their own "basis" for things and then adding whatever is popular at the moment on top as an extra choice for the user.
Also, I just remembered - cartridges, CDs, or no physical media at all? ;) What does the perfect Nintendo system have? I'd probably say both would be "perfect". Maybe there could be cartridges again equipped with special chips, like the Super-FX chip! That type of functionality is lost with the mini-SD cards of the Switch. Being able to upgrade games through their cartridges could offer awesome benefits. Although, I'm not sure how that would be handled with digital versions of games...