The more interesting question to me is actually a different one. What publisher/developer actually wants to be a 3rd party to an ecosystem? EA and UBiSoft already show their answer in the PC gaming space by avoiding STEAM and actually having their own platform. A similar move in the "living-room" and it might have serious consequences of when it comes to the royalty business model. Imagine a scenario, where publishers will stream their content directly to a television, without the need of a further middle man, like a console company. Publishers could have their own "TV"-channels/storefronts and no need to pay royalties. We know who will get into serious trouble in this scenario...

They still do quite well with their handhelds, so shouldn´t they just focus their efforts (marketing and development resources) towards their handheld business, instead of giving part of their revenue to Sony? After the same logic?

pretty much correct. That what I would do if I were Nintendo.

My selfish side though wants Zelda on my playstation :D

I do wonder how much will the other ventures such as the theme parks, anime, mobile, TV shows, films, merchandise, misc. (Nintendo-themed cafes, events, etc.) will impact Nintendo's core business, especially once NX comes around. We've seen hints of raised awareness through amiibo, Pokemon Go, and a few other things such as Kirby's themed cafe, but I do wonder how everything will come together once Nintendo's big plans get off the ground.