They haven't announced it, we haven't seen anything yet, they just confirmed it exists and is near completion. Which just adds to my especulation that it'll be for NX. Remember that Pikmin 3 was also in development for the Wii during many, many years, and they just decided to move it to the Wii U.

Well we dont know if they assisteing on some other projects, I think there are good chance that they are assisteing on Zelda U after they complete Xenoblade X, same like they assisteing Zelda SS after Xenoblade Chronicles.

Even if they don't assisteing to other projects and they expanded their stuff, you cant expect to finish new game in 2-3 years if their 2 previous projects are developed around 5 years. In best possible case they can finish new game in 3 years, that means 2018. launch.

They announced it/confirmed it, but they didn't revealed it.

What's a point of announcement/confirmation of a game for platform that we still dont know anything official except codename, especially when they still pushing hard 3DS and Wii U!? Nintendo is still keeping all NX ofical infos, so I can't see them announcing/confirming game for NX at all.

On other hand they didn't said that's for Wii U either, that make me believe that Pikmin 4 is maybe cross platform game.

They already have Pikmin 3 engine and lots of assets that they can use in new Pikmin 4 game for Wii U, so basically they can make new Wii U Pikmin game pretty fast and without big budget. Similar like they done Pikmin 1 and Pikmin 2, it's completely same situation.

Pikmin 3 and Pikmin 4 are not same situation, Pikmin 3 was announced in 2008, 3 years later they announced that game is transitioned to Wii U, Pikmin 4 was announced now and we already know that game is almost complete which means that game is 2016. title.

It also interesting timing of announcement/confirmation for Pikmin 4, Miyamoto stated this to Eurogamer in July probably right before Iwata died, so probably Nintendo didn't wanted this intervyu to be announced (and few more Eurogamer intervyus too) till now because of Iwata death.

So why in first place Miyamoto announced it/confirmed Pikmin 4 for to Eurogamer in July!? My guess is that after terible E3 and fan disappointment, they wanted to little ensure people that there still be new games for current platforms like Pikmin 4 that is nearly completed even if did not showed it at E3.

 A good chance sure, but not confirmed. In all honesty though, I think it would be pretty shitty to keep holding a dev team back every gen to help make a game that the Zelda EAD team should have had ample time to finish twice in a row. At that point Eiji either needs to reform the team with better members, or just give the LoZ IP to Monolith Soft. 

Only the Xeno series has taken 5 years of development. I would hope for a game or two without the name Xeno in it to show up some time (well, I'd be fine with some remakes or remasters, but you wouldn't think those would take 5 years as the stories have been written). Really, Monolith Soft should be their in with Namco. Make a new Baten Kaitos or Xenosaga HD should be at the top of Nintendo's things to do with Monolith Soft right now. Expanding the Wii U's library should have been on their things to do list for at least two years now.

As far as the game being completed on two or three years, sure. But you can announce it after one year of development, and release it two years later. (Look at half the announcements made in video gaming, including Nintendo's.)