Both of them half assed third party support, only Nintendo consoles that really got third party support were NES and SNES.  If your gonna go for third party support you can't half ass it you have to get almost all of it, consumers have to feel confident that they can buy every game they'll need to on your console.  Remember when Valve shit on the PS3 and said they weren't gonna make games on it?  Sony didn't say w/e we got dozens of other third parties, they kissed ass and got them on the PS3.

But the output hasn't decreased, 2013, 2014 and 2015 are all in that range.

Tropical Freeze did not take 5 years

DKC Retuns-November 2013, Tropical Freeze-February 2014, that's 3 years and 3 months, that's the same time it took between Metroid Prime 3 & DKC Returns.

Zelda U is not taking longer than previous Zeldas, the time between Twilight Princess and Skyward Sword was 5 years, the time between Skyward Sword and Zelda U is 5 years (assuming holiday 2016 release).

Literally everything u have said about Nintendo's output decreasing has been proven false.

And how is that different from now? Most people choose to buy the Nintendo handheld and to not buy the console period. The bottom line is they simply can't support two platforms on their own and third parties don't give a shit about them. 

There are different pricing options they could have for software too to make this setup work. 

For example the way they could work with Zelda I could see it like this 

NX Portable, NX Console

You can buy the portable version for $39.99. But if you want to play the home full HD version it's $59.99. 

Now if you buy the portable version first, but later on you buy the home NX too, surely you don't have to pay $59.99 to play the same game right? Nintendo can offer the option of if you pay $20 on the eShop, you can download the home version that has 1080P + added visual effects for TV play. 

I can see something like that working on the software side. Nintendo kinda already does this on the eShop ... if you have Mario 64 on the Wii VC you can transfer it to the Wii U VC for an extra charge, but lets you then enjoy the game on the Wii U with off-TV play. 

In addition to that, I don't think NX Console + NX Portable will be the exact same system. They will share a lot of the same games and be built from the same CPU/GPU architecture IMO, but I think the NX console will likely have some kind of new controller gimmick that Nintendo will bet on to differniate it from the handheld. The way Iwata/Miyamoto are talking about the platform suggest an emphasis on "new ways to play" (read: a non-conventional game platform). 

Edit: Nvm

Yes. They could easily support themselves with their fusion concept. What needs to happen is some main franchise support from 3rd parties though. CoD, some sports titles and the like and Nintendo will most likely be a quality stand alone console.

I think it would cut their profits by a lot, they do sell millions of software on the Wii U for 33% more than their handheld games, that is gonna get significantly reduced.  And even if they do what you propose that is only $60, which is a regular console game, they would have done more work than what is done for a typical console game to get it to run on two platforms.

They could probably win back some Western third party support, like maybe just the bare minimum basics like Madden, FIFA, and Call of Duty. Don't expect any miracles though. 

EA and Activision would support the Wii U if it had the 3DS' userbase, the conundrum Western 3rd party devs are in right now with Nintendo is that the Wii U has sold like crap, whereas the 3DS has sold reasonably OK but hardware wise is so far behind the engines they work with today that its not worth the effort to make games from the ground up for the 3DS.

Devs want the horsepower of the Wii U, but they want the userbase of the 3DS ... a unified platform would go some ways in achieving that.

Who says the handheld has to be cheaper than the console? A handheld between Xbox 360 & Wii U in terms of performance & a console between Wii U & Xbox One in terms of performance could each retail for about $250 in 2016/2017. They could also perhaps find a middle ground for software prices, high-end 3DS games cost $40 and high-end Wii U games cost $60, perhaps high-end NX titles will cost $50.

There are still alot of people who may buy both, for big epic games like Zelda or Xenoblade, I would rather play on my 50" HDTV while games like Pokemon or Animal Crossing, which can be played in short bursts, I may play on a handheld during my breaks at work or while in line at a store. Or for families, get the console to play some local multiplayer with the kids, and have a couple handhelds so they can play on long car rides.

The biggest benefit for Nintendo is they get to diversify their lineup by creating new IP instead of making 2 entries of all major franchises and now certain games aren't tied down to a single device with a low install base.

Well really, I mean their library this year if we assume a unified concept and maybe throw in a few notable third party releases would probably look like this:

Feb - Kirby and Rainbow Curse
Mar - Zelda: Majora’s Mask, Monster Hunter 4 Ultimate, RE Revelations 2 
April - Codename: STEAM, Dragon Quest TR
May - Splatoon
June - Yoshi’s Wooly World, LEGO Jurassic World
July - Xenoblade X
August - Bravely Default 2, FIFA
September - Mario Maker, Madden NFL
October - Devil’s Third, Yokai Watch 3
November - Pokemon Z, Star Fox NX, Call of Duty
December - Fire Emblem If

That's not too bad, especially when you consider their handheld output this year is likely lower than a normal year for the 3DS because they're likely working on games for the 3DS successor.

Because if there's anything Nintendo learned from the 3DS its that they can't launch their handhelds at that price.

Tbh I consider myself a really hardcore gamer and even I wouldn't buy both, I don't think that fanbase is very big.  There's even some Nintendo gamers that are rather young and there's no way they are getting both if the consoles play the same games.  

If they want diversity they should get third parties since they make the sport games, mature games, etc that Nintendo doesn't.