We do have some concrete information from Iwata. 

http://www.gamespot.com/articles/nintendo-s-next-console-and-mobile-will-be-like-brothers/1100-6417496/

"The point is, Nintendo platforms should be like those two examples," Iwata said, referencing iOS and Android. "

"However, because of vast technological advances, it became possible to achieve a fair degree of architectural integration," he explained. "We discussed this point, and we ultimately concluded that it was the right time to integrate the two teams."

"Iwata specifically called out the difficulty of porting a Wii game to 3DS, saying it would require a "huge amount of effort" because the software architecture is "entirely different." The same issue crops up when Nintendo tried to port 3DS games to Wii U, he said."

"However, we are hoping to change and correct the situation in which we develop games for different platforms individually and sometimes disappoint consumers with game shortages as we attempt to move from one platform to another, and we believe that we will be able to deliver tangible results in the future."

Sony isn't the only that decides how long it lasts.

Retailers aren't going to keep gifting Sony valuable store shelf space forever. Have you seen some Vita sections at retail? It's a disaster zone.

Probably by the end of 2016 most/many retailers will start phasing out the Vita section entirely in North America anyway.

Like for example I can't even find the stand Vita charger in many stores anymore. I lost mine and it was a pain in the ass tracking down a new one.

Of course it will help with stuff like they only have to develop Mario Kart 9, and they can downscale it and tweak it to work for handhelds. Just like they did with SSB 4, except it would require less resources. And there's the thing, you used the unified arch etc. as an explanation for more power in Ninty's next handheld, but when the Wii U is more than 60 times more powerful than the 3DS, yet they still managed to pull off dual development of SSB 3DS and SSB Wii U, the NX HH doesn't need to be all that close to the NX HC for it to support cross-development and porting etc. This is of course depending on what specs the NX Hc.

The difference here is that Nintendo intends to make far more games cross-titles. As explicated by. 

"However, we are hoping to change and correct the situation in which we develop games for different platforms individually and sometimes disappoint consumers with game shortages as we attempt to move from one platform to another, and we believe that we will be able to deliver tangible results in the future."

If their hardware is vastly different then you will have compounding problems because you are just developing so many more games for both platforms, rather than just one. It would make very little sense to have similar architecture, but then have the home console bottlenecked. 

We should at least expect the next HC hardware to be comparable to PS4/XBO, as Nintendo hasn't ever made hardware less than the previous generation. Wii was more capable in some ways than the Xbox, Wii U is more capable in most ways than the PS3/360. I can only think of the NES releasing with hardware less capable than its predecessors. 

When they confirm that VGC undertracked Vita by 65m units and the Vita actually beat the 3DS?

Dreamcast had a run of 9 years of official 3rd party software releases. Though the close alignment with Arcade hardware facilitated that. There are a few factors involved. I mean digital distribution means the PSP s still getting the odd new release. It really depends as much on when Vita owners stop buying software as anything else.

Nintendo is pretty much irrelevant in that. With it's harmonisation with the PS4 architechture and the current boon in lower budget/less demanding software, if they don't release a successor, it makes sense to keep it about until then as long as the figures add up. Third parties will view it the same.

People keep saying as soon as NX hits, 3rd parties will switch over, but that's not necessarily the case. Sony might turn around and do like SEGA did and drop licensing fees etc. meaning the Vita would still be a more desirable platform to develop even though a more powerful alternative could be on the market. This forum constantly views everything as black and white, the probem is, the answer is usually grey.

I think 2016 is its final year . Sony wants it to die anyway , since they say its a controller for the ps4 that was its final nail in ite coffin.

The home console wouldn't be bottlenecked. If the NX HC is as powerful as the PS4, then it would have 1800 Gflops (the Wii U has ~350). If the NX HH is close in specs to the Vita, it would have ~50 Gflpos (the 3DS has 4.8). That would mean that the NX HC is 36 times more powerful than the NX HH. Now that does sound like a lot, but think about this:

The NX HC will probably run its games in 1080p. The NX HH might run its games in 540p (I seriously doubt Nintendo will go for a 720p display on their next handheld.) 1080p means it will render 2073600 pixels. 540p means it will render exactly one quarter of 1080p, it will render 518400 pixels.

So in reality, the power gap will only be 36/4=9. And that isn't really all that much, when you consider that the PS4 is 6 times more powerful than the Wii U. So unified architecture would work just fine even with the NX HH "only" having Vita specs will the NX HC has PS4 specs.

"Presuming Nintendo's next handheld actually will outspec it. There's certainly a possibility that it won't." Is what you said. All it needs to do is match the Vita and it can take third party support, and that's what it would do at the very least, as you seem to agree on with your later posts. 

I personally expect their next HH to be between Vita and XB360/PS3, but closer to the previous, however with more ram than the latter (1 Gb.)  If the screen is qHD that would mean that it would likely be closer in multiplat (next Nintendo HC vs. HH) performance than PS3/XB 360 vs. PS4/XBO is today. 

What I think will happen is that the NX HH will be fairly close to the Vita, a bit more powerful though, but that would just entice devs to develop cross-platform.

Pretty sure they are going to try and push their phones next.