Also someone spotted a slip up from MIyamoto's translator mentioning this from the recent E3 interviews for Zelda:BOTW.So, I don't know if this is the right thread to mention this, but I can't create a new one yet, so here it goes... I found something interesting while browsing the US trademark system.
For Wii U games, you can see that in the categories for the trademark mention game discs, but not cartridges.
On the other hand, 3DS games do mention cartridges in the description:
However, for Breath of the Wild, there's something different, it also lists video game cartridges:
I don't think this is a random decision or mistake, as Nintendo has never assigned video game cartridges to a Wii U game before (unless it also has a 3DS version). However, we already know there's going to be a NX version of this game, so this could be a strong indicator that NX will, in fact, use cartridges.
This sort of corroborates the unified library they've been talking about in the past. A cartridge based system would mean games would effectively need to be bought once but can be played on the home console or portable handheld. I think this would be a great move as this would mean the NX would have a HUGE library of games as everything would be made once and played either on the console or portable. Home console Pokemon Games
It could possibly not even have an optical drive to save costs and be smaller.
but on the other hand it's also kinda 
because of course Nintendo would think of going back to cartridges again.
