According to a recent Nikkei report, Nintendo will introduce paid downloadable content to its games for the first time in recorded human history next March, with the release of Fire Emblem for the 3DS. The price of this expansion will apparently be "several hundred yen," and that it -- and other DLC on the company's platforms -- won't make it any easier for players to make their way through Nintendo's games, which probably weren't very difficult to begin with.
Nikkei also reported that the Wii U will also play home to downloadable add-ons, but said nothing about the still-to-come library of the Wii, which -- well, in order to release expansions for something, you first need something to expand upon.