The OP says a moderate leap forward, that is "some" improvement. Also the unification of handheld & console vastly increases the number of releases. It varies slightly by region but as of the end of last fiscal year 3DW has about 400 retail releases and Wii U about 100 retail releases for a total of about 500 retail releases. Also the OP said a potential new type of gimmick is possible as well which depending on what it is could be seen as an improvement as well.

Let's break it into pieces.

Straight from the OP:

"As powerul as a WiiU" and what you say with "it's in the same basic power range" is like saying that it won't surpass WiiU.

No one knows if merging both devices is a viable strategy because no one has ever done it before. It can work but it can also fail, there are no guarantees.

Also, I'm perfectly aware that how powerful Nintendo is as a publisher, but there's one caveat here with them supporting a single device: new IPs. If NX is a single hybrid console the case won't be IF Nintendo will make new IPs, but HOW MANY they will have to create. Why? Easy, unless you want them to launch twice as many Mario games (2xMario Karts, 2xMario 3D and 2D platformers, 2xSmash Bros, etc) they will have to create new IPs to avoid bloating the market with the same characters over and over again, damaging the value of those IP.

And before you say anything, of course I want Nintendo to make new games and IPs, and I know that Nintendo can create great new IPs like the recent Splatoon, but they've also made games like NintendoLand or WiiMusic thinking that those would be successes... They are not perfect.  

Sorry but, do you really believe that an NX with the same power as a WiiU will entice third parties? This is what is happening now with third parties:

• Western Devs/Publishers_ They stopped supporting handhelds a long time ago. Some still make a couple of small games for 3DS or PSVita, but the truth is that their mentality is either go big (expensive games with great graphics) or go small (mobile). There is no longer a middle term.
• Japanese Devs/Publishers_ The situation seems to be similar than in the West with one caveat: handhelds are more important than home consoles. Console gaming in Japan is almost niche (I'm exagerating to make my point), with most of the development of Japanese games targeting handhelds. The problem is that handhelds are also losing ground to mobile gaming and many big publishers like Square-Enix are releasing more games on mobile than on handhelds. And that's a trend that doesn't show signs of change. So you have big, international projects that go to home consoles because that's what sells in the west, small projects that go to mobile and Japan centric games that go to whatever platform the devs think will have more success. 
• Indies_ The way most indie studios work seems to be "make the game for one platform and then, if it's cheap enough and there's a chance to success, port it to the other platforms". Form factor doesn't seem to be a problem and neither is power, as long as there enough of it.

Now look at Nintendo and what NX will be acording to the suposition made by the OP: Indie studios are already working on WiiU and 3DS so as long as the conditions don't change, they will still work on NX. Therefore, no change. Western devs won't touch NX because it will be underpowered compared to PS4/X1, and a joke compared to PS5/X?. Therefore, the situation will be the same or even worse as some won't even bother to have games at launch to test waters. And then we're left with Japan, which I think will treat NX like they treat 3DS. So again, the situation won't change much.

Of course, NX can be so cheap that it becomes a huge success, but look what happened to the Wii. Despite being the best selling console of the gen, it was also the one with worse third party support. So selling lots of consoles doesn't guarentee third party support either.

No, anyone who thinks NX will regain third party support, specially in the conditions stated by the OP, is in denial.

Given that we still don't know what NX is in terms of hardware other than what we have speculated it could be (home console, handheld, hybrid of both or two systems with shared functionality), the discussion about if it's a replacement, a successor or a complement (a third pillar of sorts) is rather pointless.

"even if half of 3DS owners bought the NX that's still 3 times more sales then the Wii U and with Vita as their main competitor"...

If NX only sells half the numbers of the 3DS it will be labeled as the worst mistake ever from Nintendo, including the Virtua Boy. There's no way Nintendo could get back from that, it would be the end.

And of course Sony won't do an hybrid console, they don't need to.

I would if it was truly meant to be the successor to the Wii U and Nintendo's primary home console. Still sort of want it to be the next handheld device myself.

A post from the OP himself

"Well anything can play third party games. The Wii U can play third party games. This is operating under the assumption that it's a hardware that's only a minor bump from the Wii U (as the Wii was from the GameCube) but has the added functionailty of real portable play. "

So no you're wrong in how you read the post as this flat out proves you wrong on that account, no one knew whether motion controls would be a huge success either difference with a hybrid system is that the portable market has a clearer path then what the Wii did so it's a good time to take the risk then when the is actual hot competition in the like with consoles. Your part on new IPs is a strawman argument as the point of one platform is to remove the need to create new installements of the same franchise for two platforms, you'd only have one MK and so on which would free up the teams for other ventures and franchises, that's the whole point. They can't do that as much now because once 3D Mario is done for handheld it then has to be done for console for example.

Yes a hybrid console would attract third parties more then a far more powerful Wii U successor you know why? The portable market, 3DS has already proven that developers are more keen to develop for it then Nintendo's consoles, Square has like7 games on 3DS including a DQVII Remake and a KH game but only one on Wii U. Your whole attempt to say no one develops for handhelds is laughable it's like you improvized any old argument because for a start portable gaming in Japan is far from niche with around 20m 3DS' sold that part alone blows your whole stance to bits heck even Vita is doing well there. Games like MHX, Bravely Second, Yokai Series, DQVIII, Theartrythm Series etc... highlight that eastern developers are still very much on board, western developers have never been keen on portables to begin with so that makes little difference and no Indies don't just stick to one platform in fact it's the opposite in where they want to hit as many platforms as possible.

The's only one alternative to Nintendo portables in Vita and that doesn't get the likes of Pokemon and such which are the heavy hitters in the market, if half of 3DS owners bought NX it would more successful then Wii U, GC and N64. Only Wii, NES and SNES as home consoles would have sold more, Their home consoles are inconsistent in performance but their portables are consistent each hitting at least 50m which if the NX is a hybrid and hits that mark that's more then even the SNES. I wouldn't be surprised if they pushed the portable side of things and let the console side of things just ride the success.

But you are agreeing with me, no one knew if motion controls would work and no one knows if the supposed hybrid device will work too. Until someone does it, it's only a bet that can prove a success or a failure.

And now, allow me to ask you to reread my post as you asked me to reread the OP. I never said that handheld gaming was niche in Japan, I said that console gaming is niche. And then you just go and agree with me that NX will only have the same support 3DS and WiiU have, not more. Thanks.

Also, I said that indie seems to work first on one platform (their main one), and once they have launched it, then port it to all the other platforms that they can. And, I also said that they are already developing for WiiU and 3DS, so NX won't improve that either.

Trying to use nombers on a sales focused site... Nintendo64 sold 32 millions, that's more than half of 3DS, although the handheld will end beating her too. And yes, so far every Nintendo handheld has sold more than 50millions, but if we look at the pattern (GameBoy_ 119 mil, GameBoy Advance_ 82mil, Nintendo DS_ 155mil and Nintendo 3DS_ 53mil and rising), NX doesn't have those sales guaranteed.

You mean same like Wii was death of Nintendo consoles!?

Think about something similar like Wii U gamepad, you have on gamepad FWVGA (854x480) resolution and on TV 720p or 1080p resolution.

NX will definitely have better CPU probably ARM, more RAM is very likely and little modern and better GPU. That would be enough for 1080p Nintendo games.

I think Wii U has proven us that power alone is not important if the software outpu lacks ambtions. I prefer a Wii style hardware but with awesome ambitious games like Super Mario Galaxy, Metroid Other M, and Skyward Sword.

If that happens then sure, let's hope Nintendo can deliver something compelling.