NX collectively is both a handheld and console. It's just a matter of which one Nintendo releases first because there's a case to be made for each. On one hand, Wii U is languishing. Nintendo should try to replace it with a worthy and more importantly finished successor sooner rather than later. On the other hand, Nintendo essentially has the handheld market to itself again with Sony essentially bowing out quietly. Nintendo should be trying to protect that market with a successor as 3DS has been showing its age and New 3DS hardly picking up the slack. Wii U at least has a major holiday release as it continues to tout Zelda as a Wii U game though I think we can expect an NX version. Currently, 3DS has nothing announced for Q4.
Personally, I think NX-Console should launch this year (if not both) since Wii U is in such bad shape, but NX-Handheld is probably more likely. New 3DS, as expected, didn't rejuvenate sales the way Nintendo hoped it would. To date, it has one exclusive. Nintendo knows what its money maker is hardware-wise and will try to capitalize on it.