http://www.nintendo-insider.com/2016/08/kingdom-hearts-3-rumoured-for-nintendo-nx/

Apparently EB Australia had the game listed briefly. Squenix is really looking like a strong supporter of NX.

Oh gosh, I hope that's true. I would def buy it on the NX. Make it happen SE

Someone probably just ticked a wrong box. I really wouldn't read into this. As it stands, it hardly makes any sense that the game is releasing on Xbox One after they have gone to such lengths to consolidate the series to the Playstation line since last gen. Just tossing the third numbered but really something like 10th game in the series randomly on the NX would be silly at this juncture unless SE decides to voice plans to bring the PS3 HD Remixes to the current gen.

Also, top kek to the article somehow thinking that the lack of KH3 news is because they are holding off until announcing it for the NX. In what universe does it make any sense that they would withhold all details surrounding the game over a port to a mystery platform? We aren't getting details because the game is still crawling through development. I'm sure we'll start seeing a lot more about it once FFXV is finally out of the gate since it is the next huge SE project that is likely to be released, barring unexpected massive progress on the FFVII remake. In the mean time, it would be awesome if silly Nintendo loyalty didn't breed such poorly thought out articles.

Doubt it's happening, but I'd be happy if it is. KH3 was the only game I really wanted a PS4/XBone for, so if this is true it'll basically save me 300 bucks.

The series goes...

PS2-Mobile-GBA-PS2-DS-DS-PSP-PS3-Mobile-PS3-Mobile-PS4

The series has a fairly strong presence on Nintendo systems, and as you pointed out, they're putting it on the XBox One anyway.  Assuming the NX is reasonably easy to port to, there wouldn't be any reason to avoid it, particularly since Kingdom Hearts has always been fairly popular with younger fans.

I wouldn't be surprised if this was real since KH has been on Nintendo platforms before

The murmurs are Square-Enix is going to support the NX big-time.

I've said before, for Japanese developers a portable machine that's capable of even approximating console level graphics/engines is a game changer.

Maybe?

You missed Dream Drop Distance :P

Nintendo handhelds =/= Nintendo consoles, and as I mentioned, SE made a pretty grand effort to consolidate the series onto Playstation last gen. On two discs, I can play (or watch) almost every KH game released, and they are continuing their efforts with 2.8 coming to PS4 preceding KH3 primarily meant for PS4. It isn't hard to see that even SE recognizes it makes sense to have all the games + the whole story accessible at least within a single series of consoles, and they have even said bringing the Remixes to this gen isn't totally out of the cards to potentially consolidate the entire series onto the PS4.

Now, if they do bring the Remixes forward, I could see an NX release of KH3 being feasible as then the whole series could potentially exist on PS4, Xbox One, and NX, maximizing series exposure. If they don't though, making an NX version based on "SE made handheld focused games for Nintendo because Japan loves handhelds" isn't the most compelling reasoning.