Random thought.
Nintendo is known to return to their (and not only their) old ideas occasionally. GamePad was a reiteration on GBA/GC link cable. 3DS was reiteration on something they tried with GameCube. StreetPass was a reiteration on a DS game gimmick from something (Dragon Quest? Not sure). And the whole hybrid library concept could be seen as reiteration on GameBoy Player and SGB.
One of known abandoned elements of DSi is that it was supposed to have two cart slots for some reason. Is NX home SKU, among other things, Sufami Turbo HD? Note that this would be a relatively cheap-to-manufacture gimmick with card slots, but relatively complicated with discs, and Ninny doesn't want to get a reputation of pushing digital, not after the 180. Of course one could say that a lot of games unlocked extras without need for such a feature, but it could be more interesting if there was a global framework of things that games are supposed to share (textures, humanoid characters, simple maps...).
Or maybe it's something completely different like all physical games in amiibos I don't know