Another stuff about Nintendo console is that developpers have to deal about fighting at the same place as Nintendo software. How would a new Third Party Competitive TPS on Wii U when there is already Splatoon available ? How can anyone make a plateformer 2D with New Super Mario Bros in front of it. Even Donkey Kong suffer from that !
It's a lot harder than it seems and there is no solution for that for Nintendo.
This argument was always nonsense. Nintendo's systems have frequently suffered software droughts, to the point where a 3rd party would have ample space to release games in these genres. The truth is that the major 3rd party publishers have completely moved away from the genres and demographics Nintendo pursues. In the case of Splatoon, a major 3rd party would never directly target an all-ages audience for a third-person shooter the way Nintendo have with Splatoon. And even if they were targeting the same demographic, so what? I don't see 3rd parties suffering on Sony platforms due to the existence of Uncharted, Infamous, etc, and those are series that directly target the same genres and demographics of EA/Activision/Ubisoft.
The truth is that Sony and MS have made platforms that cater directly to the demographics that major AAA 3rd parties want. 3rd parties don't target Nintendo platforms because they would have to put in the work to create that marketplace on Nintendo platforms, and they see that as unnecessary risk when they can reach enough console/PC users on the platforms they do support. Nintendo will need to prove this market exists before major 3rd parties will give serious support.
Nintendo's real 3rd party support will come from Japanese/mid-tier Western publishers and indies, before the likes of EA/Acti show up. With the recent success of Japanese publishers in the West via Steam, and the "second wave" of larger indie titles coming from crowdfunding projects and growing indie studios, Nintendo would have a pretty good base of 3rd party titles to put on their system. They'll need to start from there, the same way a platform like Steam has had to constantly prove the existence of certain customer groups before major support comes down the line. Nobody doubts that Nintendo targets family audiences really well, but no major 3rd parties outside of mobile dev/toys-to-life invest in that demographic anymore.