There are rumors that the NX will be a hybrid of a console and a handheld. However, I'm not really sure how this will add up because they are looking to rival the current generation of consoles with PS4 and XBO being way above the Wii U.
It's possible that they will do something to integrate a handheld into the console in some form, but I think Nintendo will try to go back to their roots and be a dominate core gaming platform on consoles like they were with the NES and SNES. It's possible that with this we will see a boost in console sales as well because Nintendo is such a beloved brand.
The speculation is that it's either going to be a hybrid or it's going to be a brand new ecosystem that has several different platforms (console and handheld in this case) that share the same architecture, operating system and play the same games. It's what many think it will be as Iwata has talked about doing something similar to what Apple does (iPhone, iTouch, iPad, iTunes etc.. are all brothers of the same family). This is why the recent patent of no optical disc drive makes sense as in order to play the same game on a handheld and console, you use carts instead.
Whatever it is exactly, everyone seems to speculate and agree on one thing. Nintendo NX, hybrid or multiple platforms, will play the same games. That's important because right now Nintendo's 3rd party support are Japanese developers who make games for their handhelds. On top of that, Nintendo has been having severe 1st party drought issues and so making games for one platform can improve their output a bit. There would be that much needed sense of consistency.
My thinking is perhaps in order to save the home console market and make it healthy again, it's just simply a matter of putting those types of gaming experiences on a handheld instead of a console. It has to be done right though. That's the key. I don't think people want a home console experience like Mobius Final Fantasy. When you look at the PSVita, that market never materialized because the games they want are not cheap to make and won't get the sales they need. It's better to make those types of games for a home console instead.
What NX would basically be doing is hitting two birds with one stone, or two markets with one platform/platforms that play the same games. Developers who want to make something expensive can do so knowing that it will be playable on both a handheld and console. The game will not be restricted to just one market that way.