In a questions and answer session with industry analysts, Satoru Iwata from Nintendo confirmed that free-to-play titles and a micro transaction model for Wii U titles is possible. There is no technical reason that a developer or publisher could not leverage such a concept on the Wii U.
The Digital Rights Management system that Nintendo has been designed from allows developers and publishers to take advantage of things like free-to-play and micro transaction revenue models. Developers will have the option of releasing titles on either optical disc or digital download formats. Titles in the digital download format, however, will not be ready for launch but will come via an update later.
Apparently, Nintendo isn’t considering the development of a first-party, free-to-play title at this time, but you never know what might be in the future, as digital downloads can add additional profitability and lessen inventory risks and save on the shipping of physical copies of a title.
From what we know, right now there are not yet any plans for a free-to-play or micro transaction titles that are in development for the Wii U from 3rd party publishers. However, some publishers have told us off the record that the possibility of trying a free-to-play micro transaction title on the Wii U is definitely something that they are at least thinking about.
Read more from Iwata about this here.