Actually 3DS and Wii U dont share almost anything, they are completely separate platforms, with seperate OS-s, separate account, different architectures, different games..

What Nintendo said they want to do with NX is to make unifed platform like iOS or Android, imagine iPad like home console and iPhone like handheld and you get picture what Nintendo is aiming for. Also such a platform doenst mean just a same game that will be playable on handheld and home console, such a platform can heavy integrate home console and handheld, so for instance we could use handheld like controller for home console or something diffrent.

Such a platform will be much more attractive for users than separate platforms like before, for instance NX home console will be much more attractive because you will have handhelds games on it too, or handheld will have some home console games too, that means such a devices will be much more attractive for consumers than just home console that has only home console games or handheld that has only handheld games. Also I dont think that every game will be cross device game, there will still be some exclusives but definitely biggest number of games will be for both devices.

Why Nintendo is going for unifed platform!? 

Because in modern age when games require much more resources and development time than before, they cant effectively support two totally different platforms. We already saw this gen when Nintendo struggled hard with constant software droughts and delays, while Sony for instance completely abandoned Vita.

So instead losing time and resources on making two different and separate NSMB, Mario Kart, Smash, Yoshi, Kirby...games for each platform individually, Nintendo can make just one game instead of those two and use that extra time and resources they have in that way and make some other project. That will leave to higher output of games that Nintendo can provide and to much more diverse lineup of games.

Also this could be very attractive for 3rd parties as well, they could develop games that would be sell on two devices in same time.

So yes, it necessary for Nintendo and IMO this is very good plan.

Handhelds are dying, there's no point in NIntendo wasting their fortunes trying to avert the inevitable. Better to invest in a market that actually has a future. (Consoles)

Here we go again. Killing before conception. Give it a rest. I know we're all in a frizz about NX but until NINTENDO says something about the console's concept, I'm not going to deem how worthy or unnecessary it is. Not yet, not while only 1% of info has been confirmed by Nintendo.

       Is NX even necessary if all Ninty is doing is making a platform that can handle multiplats? Why exactly would Ninty need to make their plats more integrated if 3rd party support is all their after?

       So in order to answer this question we need to first know what NX is for. The only thing we know for sure about NX is simply its suppose to make Nintys handheld and home plats much more integrated. How much more could Ninty's plats become more integrated? 3DS and WiiU already share alot, alot of the same franchises even some of the same games(Smash, Hyrule Warriors). Cross buy is already a thing and it only makes sense between the same games(see Smash dlc). Cross buy wouldnt work very well for say MK7 and MK8. Are they talking about more franchises crossing over from one side to the other? If so, wouldnt that be a more internal theme in Nintendo? Porting franchises back and forth is hardly something to name as the headlining theme of your plat. That was the point from the very beginning, starting with Gameboy playing portable versions of the NES games. Now you can take your favorite franchises with you on the go was clearly the GBs selling point, so what would be so different now? The OS are more or less the same, Miiverse is no longer exclusive to WiiU and has been that way for a while now. So what is so much more integrated about NX? NXs integration has to be even further than all of that. Why would Ninty take such a leap, just to gain 3rd party support for their home consoles? When has Ninty shown so much love to their home console side? This leads me to my next issue with so much home console bias.

        Wouldnt this also make Nintys handhelds less attractive? NX being even further integrated than what I described above just doesnt make any sense. The home console would be significanly more attractive and lead to less handheld sells due to all the over the top integration. Even if the integration isnt over the top, all the exclusives the handhelds had would be loss. Leading to more lost handheld sells and a less attractive handheld making it even easier for smartphones and tablets to further erode the dedicated handheld market. So now NX not only has to make up for the dying home console side of Ninty but also the further decreasing handheld side in an even more competitive space? Good luck with that NInty! Nintendo would probably loose their strong hold on Japan because now things are on even playing grounds with Sony. So all in all Ninty would be producing a less attractive handheld all for a more attractive home console in a market Ninty has some very strong consistent competition? When the truth is Ninty pumping out more games for home consoles is unnecessary if 3rd parties are on board, because 3rd parties would already have it covered.

       Basically people, wouldnt it make more sense for Ninty to instead shift more resources towards their handhelds and let the 3rd parties do all the work? Why not try to save both sides? Resources need to be shifted towards the handheld side due to the war against smartphones, while 3rd parties can keep the home console side afloat with the occasional Ninty first party major release sprinkled in. It would be 90% to 10% in favor of handhelds due to 3rd parties not being there to support it. The home consoles would still get things like MK, NSMB, 3D Mario, 3D Zelda, 3D Metroid, Star Fox, and ofcourse Smash. The handheld side would just receive everything else making NX unnecassary. Further integration only leads to a less attractive handheld in this scenario of NX attracting 3rd parties. Im not even convinced a home console from Ninty would sell more than 3DS!

That's the question you should be answering. NX isn't necessary if attracting 3rs parties is all Ninty wants. They could continue to make two distinct plats with 3rs parties making home console games and Ninty focusing on handheld output. What is different dude about Wiiu and 3DS? I never get examples, yet I give examples. Miiverse and you can now link profiles(unified accounts) already. Why are people like you trying to downplay their integration(WiiU and 3DS)?  3DS can already be used in Smash as a controller lol, if that was a big deal they would take it even further in their current plats. Crossbuy already exist to some extent but it's not that necessary in plats that have different libraries. What you're preaching is stuff Ninty could already do. You mention a more attractive plat to 3rds, so you expect a handheld that can handle XB1/PS4 support? I would love that but that sounds unlikely, which brings me back to the point of the thread. The question I left remaining in the op.