Problem is, Wii U isn't the outlier here. The success of the Wii is the anomaly and the trend for Nintendo hardware sales is going down generation after generation.
If the Wii U's failure in a vacuum isn't enough to rethink their business, then the trend is.
With their move to mobile anything is on the table right now. Their fans have been happily putting their fingers in their ears and casually dismissing the idea of mobile development or third party development because they really aren't understanding the true implications of new products like Amiibo or the Universal theme park deal.
Nintendo are once again trying to get themselves into a position where they aren't relying on their dwindling hardcore fanbase and they seem to be taking any means necessary to do that. Is a move to third party development part of that? Who knows but you'd be foolish and/or ignorant to rule it out.
Can it happen? Yeah. Will it happen? I imagine it happens after at least one more wii U level failure...and even then.
Going 3rd party isn't this amazing move, people. It is you as a company admitting you aint shit and thus need to kill one of your branches to save yourself. You don't willingly give up power unless you really really have to.
The Nintendo that goes third party will be in a lot rougher shape than people imagine. They won't and shouldn't do so until they have to. And if they can keep making a profit with the level of disaster the Wii U is, then I expect it won't happen for a while.
I'm not saying it will never ever happen, I am saying that it won't be this sunshine and rainbow scenario if it does.
3rd party Nintendo is not current Nintendo but on more consoles. Many franchise will effectively be dead. Many of the actual development teams will be cut down. And I question if there will be this big boom upon release on new consoles people expect...or will these titles still sell wii U release numbers or worse.
I really think the number of people who would legit quit gaming out of fanboy rage, those who NEVER were interested in Nintendo games and such is not being taken into consideration here. I think the number of people who are interested in Nintendo games but not enough to buy the console isn't this large untapped crowd...I feel as if many of those will find another reason to pass on buying their games (mainly y'know not being the only games on the block competing for time anymore...the reverse reason 3rd party companies don't release games on nintendo systems allegedly).
But again I am not saying it won't happen...I just question if it is that great of a thing for gamers, nintendo fans, Nintendo themselves longterm (key word, because short term it would be awesome to play Nintendo games on my ps4, I'll admit that...but longterm I fear that it wouldn't be sustainable). I feel the same way about them releasing Mobile Games. It'll be great for profits and short term gain...but I wonder if it will eat into their handheld division.