Nope, won't happen because the Wii U sadly isn't capable of running of this game. Remember the game is being developed on the Unreal Engine 4 which doesn't support the Wii U. Even if they ported it to a different engine, do you really want to go through watch dogs, ghost, and black flag all over again? 

It wouldn't outsell the PS4 version, could outsell the X1 version but I'd doubt for a simple. Obviously theres an audience on the system for this game to do like 2-3m on the Wii U easily (more so then the X1 audience). Problem is most fans, even if they had a Wii U would get it on PS4. I mean if you want KH3, you probably want FFXV and probably certain other Japan PS4 games as well which means getting a PS4. Once you have a PS4+Wii U then you're not going to pick up KH3 for Wii U are you? So in actuality I think it'd just about pass 1m, not through lack of interest but through the PS4 version cannabalising it.

If it came out today this wouldn't apply so much, but the game won't hit shores till 2016 at the earliest.

Unless Nintendo is funding the port it won't happen though. Square are not going through all that effort to port it to Wii U when anyone who wants the game is going to find it anyway. Thats what system sellers do, they make people buy the console the game is on

The xbox360 gpu is about 20% as powerfull as the X1. Wii U's gpu is at least 50% as powerfull as X1, being pessimistic. In the end, there's no game put on ps4/x1 that wii u can't get a port.

Yes, and would imedeately make Kingdom hearts 3 more likely in the future.

Eh, no...   http://www.ign.com/wikis/xbox-one/PS4_vs._Xbox_One_vs._Wii_U_Comparison_Chart

Wii U GPU is 0.352 Teraflops the XBOne is 1.31 Teraflops  the XBONe is ATLEAST 3x more powerful. As I said there is NO WAY (at a decent resolution) to make a Wii U port of Kingdom Hearts 3 if the XBOne is not 1080p with solid AA. I do not think a dev is going to make a game below 720p.... So it will never happen.

That is not even to mention the Wii U clock speed is way slower and has less shaders and probably inferior ram (I am not sure how ram works in the Wii U so I can not say for sure). To be exact all DDR3 ram is slow and terrible for gaming, the XBOne and 360 both have specialized ram to try and make up for that fact (and they do for the most part)

Wii U's gpu is NOT 0.35 teraflops. Even if it was, it would still be portable, albeit with more difficult. the clock speed mith isn't helping your argument either, especially when wii u's gpu is built to do some cpu functions.

That would weaken the graphics performance even more..... Show me a valid link where it does not say the Wii U GPU is 0.35 Teraflops...

http://www.gamespot.com/forums/system-wars-314159282/gpu-specs-comparison-wiiu-vs-xbox-one-vs-ps4-30976500/

As I said it is atleast 1/3rd weaker than the XBOne. KH3 is technically impossible on the Wii U unless they make it at a pathetic resolution for 2015. That is to not even mention the slow ram which is roughly 6x slower according to this 

http://www.extremetech.com/gaming/156273-xbox-720-vs-ps4-vs-pc-how-the-hardware-specs-compare/2

CPU wise the Wii U would be fine as neither the PS4 or XBOne has that much CPU power

You show me a valid link saying it's 0.35 teraflops. But don't waste your time because that isn't true. We have no confirmed numbers for wii u's gpu (0.35 tflops is jus a random lie) but it's performance on the exclusive games says it all: it can get a port of any ps4/x1 title.

I have most Nintendo Wii U games and have not seen a single game that looks much more impressive than games on my PS3.....

The Wii U GPU is 0.35 and less than 1/3rd as powerful as the XBOne, but I guess every website is wrong and a random guy on the internet is correct. Teraflops is not the end all for graphics but the combination of way less shaders, way less ram and inferior ram, and the slow clock speed come together to make the Wii U GPU atleast 1/3rd weaker (probably closer to 1/4th)

1080p takes roughly double the power as 720p. But if the game is 900p/720p on the XBOne it would have to be an absolutely pathetic resolution on the Wii U. That is not even taking into consideration that the ram is roughly 6x slower. KH3 on Wii U is impossible

I think you haven't seen Wii U games from nintendo, then.

Every website? lol, Wii U's gpu isn't 0.35 tflops and you can confirm that anywhere. Nintendo never revealed the specs and those are just made up numbers. But as I said, wii u's exclusives show us what it can do.

Oh, interesting thing: You said it takes double power to render 1080p instead of 720p. well, wii u has smash bros at 1080p and 60fps. That's twice the resolution and twice the framerate of most ps360 games, two consoles with roughly 0.2 tflops gpus.