Actually it seems to be a portable console... there are android rumors, Iwata said that Nintendo will continue making Wii U games after the NX, there was a guy who worked on a mobile windows OS that is working on NX, and its gonna be less powerful than the PS4, and the 3ds is 6 years old.... Everything seems to be pointing in the direction of the NX being a portable.
Edit: it still could be a hybrid.
There was also this job listing from Nintendo looking for a lead engineer for their next-gen hardware, note is specifically says that
"Low power and SoC design experience would be a plus"
That hints strongly at a mobile system on chip.