In the end I don't see things turning around for Nintendo with third parties for a very specific reason. The make up of the user base. Nintendo themselves has game series that if released would go a long way of helping to cultivate an audience that would be more open to buying third party titles in larger numbers. However Nintendo will not release those series because they aren't huge million sellers. Some like to talk abou the mid-tier game possibly being a thing that could help Nintendo. Well Nintendo themselves has games that could be classified as mid-tier games but will not release them.
Now Nintendo has some of that audience already but not in large enough numbers. They aren't engaged enough to be around regularly I think. They show up and buy the latest 3D Mario, Zelda, and maybe Metroid or another exclusive if they're lucky and then go back to playing their PS3, 360, or PC or before that PS2 or Xbox or PC.
It does not matter if the Wii U sells well this holiday on the back of Super Mario 3D World or Donkey Kong. That isn't the audience third parties want or will find attractive. In order for Nintendo to actually build that audience they would need to resurrect some of their past games like Star Fox, F-Zero, Metorid Prime, Wave Race, Eternal Darkness. Release them with online multiplayer and actually release sequels to them. Perhaps release two entries on the WIi U and actually push all of them in the best way they can. Accept that there is a market for NIntendo games that aren't related to the Mario franchise. These games won't sell over a million at first. They didn't in the past. However they could nurture them and get them to grow over time. However to do that they need to keep customers engaged. Which is why they must release multiple entries over the Wii U's life. These aren't going to be evergreen titles and nor should they be. They have to be treated the same way third parties treat their titles. Titles to be played and enjoyed for two years and then move on to the next one. Titles where the focus is on online multiplayer and not local multiplayer. Titles that still have the Nintendo charm and spin but aren't platformers or aimed at everyone but a specific market.
Then and only then do I think third parties will change their outlook on Nintendo hardware. They'll see that Nintendo is series about building a user base that that they can engage in a meaningful way.