please, another donkey kong country!
if not, only metroid can fill the emptyness.

I like the DKC series, but I'm not sure if Retro is the right developer for it. DKC: TF was a bit too hard IMO, the DKC series should have some tough platforming but should generally be relaxing as well, I dunno.

Maybe give DKC to the guys who do the Yarn Yoshi/Kirby games but keep David Wise on for music. 

What I think would be very useful is if Nintendo were to invest quite a chunk of money into expanding Retro and opening more development studios, that way Retro can hire more employees to not only get games done faster, but can work on multiple projects at once. Maybe they can have 2 branches of development within Retro where they both work on DK and Metroid simultaneously. And maybe have the occasional new IP here and there.

Edit: Actually, they could do this with all of their subsidiary studios. I mean, aside from Xenoblade Chronicles X, I can't think of any other game that Monolith Soft has been working on.

I disagree, Donkey Kong represents the hardcore platforming  for Nintendo in the same way Kirby usually represents the more light casual side, and I think is totally fine as it is.

As for the difficult, yeah it was very challenging but it is nothing overwhelming at all, my little cousin is a 10 years old girl that never plays hard games and she managed to finish the entire game by her own, she suffered trought it, she spend a lot of time until she finished it, but the game was so fun she wanted to try again and again until she succeed, I think if my little casual gamer cousing could do it, an adult should have no problems at all, in my case the heavy but fair challenge of Tropical Freeze is an important part of why that game is a masterpiece, it makes sense with how the game is, for relaxing platformers we already have Yoshi and Kirby as you said, and they are enough.

I have very complicated feelings about the Returns games. I don't actually don't think they're too hard at all, but I absolutely don't think they are Country games. The gameplay is completely different, the artstyle is completely different, and perhaps most importantly the atmosphere is completely different. I think that I would be happier if they were called something else, like Donkey Kong Returns or something.

In other words, I think the games are pheonominal, and I don't mind Retro making at least one more, but I wish they just called it something else because they have absolutely nothing to do with the original trilogy outside of being 2D platformers. It's the same reason I'm okay with Metroid Prime. If they called it Metroid 4: Prime, it would aggrivate me, because they play nothing like those games or really any Metroid game. Prime is one of my favorite games of all time, but a big reason I can stomach its vast deviations from the core aspects of the franchise is because it simply branded itself as a side series.

Dont expect new DKC 2D game any time soon, I think Nintendo will take little break with DKC 2D but DKC 3D would be welcome.

Look at Spemanig thinking he's superior gamer by saying the new Donkey Kong games are not hard, give it a break son!

They had the next Metroid (?) scheduled for a late 2016 release on Wii U. Then Nintendo decided to launch the NX in late 2016 and approached Retro to redo the game for the new platform instead. Because of this we didn't see their new project despite the twitter teasing.

Traditional Metroid game for Wii U pls

Not too hard. Learn to read.