During a Q&A with shareholders, Nintendo CEO Satoru Iwata was asked how Nintendo intends to gain closer third-party support for the Wii U and 3DS (via Siliconera). He replied thusly: “We think it very important to make several hits from the third-party software publishers within the first year from the release of the platform, while offering Nintendo software seamlessly. In order to achieve this goal, we have shared information about the new hardware with the software publishers earlier than we did previously and built a cooperative structure, and we are developing several titles in collaboration with these publishers.”
As these things often go, he would not go into specifics: “I cannot talk in detail about the names of the titles, or with which publishers we are currently collaborating, because we have not announced this information yet, but what we are aiming for with the Nintendo 3DS and the Wii U is platforms that have much more software, and a wider variety of software, than the former Nintendo DS or Wii.”
So far, there has mostly been some vaguely positive noises (like here and here) coming from third parties regarding the Wii U, but very little in terms of concrete announcements. Question marks over especially Wii U third-party support will likely remain until more solid evidence arrives.