Changing their policies and poor communication has to be the first step. Even if Wii U was closer to PS4/One, third parties would still tell Nintendo to take a hike until they start treating their partners better. I'm not claiming that better hardware wouldn't also be great, but Nintendo has proved in the past that third parties will support less powerful hardware if there's money to be made. Nintendo stuck with Gameboy for 37 years and DS trounced PSP. Opting for lower spec hardware is perhaps an additional barrier though one companies have overlooked in the past in favor of profits. If Nintendo can include higher specs and do so responsibly, they absolutely should. That's a topic for another time though. (I might finally write that topic tonight)
Ultimately, it's give and take. Nintendo shouldn't have to bow to third parties, but better communication is a reasonable request. I wouldn't even consider it a concession because it should go without saying. This is how to build stronger relationships. Since forever, Nintendo has just demanded things. Nope, back away not today, Disco Lady.
Nintendo is slow to change, but they've been known to be receptive to criticism. I'm glad Pete Hines from Bethesda put Nintendo's BS under the spotlight. For too long, third parties would regurgitate nonsense like "The controller is too unique." What? We all kind of knew Nintendo's policies were antiquated and sucky, but we would mostly hear anonymous murmurs. Now, Nintendo can't pretend it's not a problem. This time they got called out publicly while their console is struggling. It's pretty obvious what they should do. It's unfortunate that it should get to this point, but if it works (and hopefully, it will), so be it.