A new marketing leaflet seen in the wild seems to suggest that the Nintendo NX could in fact be called the Nintendo Duo.
Rumours are that the NX is both a handheld and home device, so perhaps the name Duo would make sense.
This of course is all rumour and speculation for now and we can't take the word of an image found on 4Chan. But still, it's worth mentioning just incase.
It's likely fake, but we'll see.