This isn't the first time that we have had this rumor: http://www.neogaf.com/forum/showthread.php?t=1215139
But our fellow Gaffer Atheerios found this:
Originally Posted by Atheerios
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.
What do you guys think? It is interesting that Zelda BOW mentions BOTH discs and cartridges. However, Ever Oasis mentions game discs and it is a 3DS game....soooo this might not mean much.