It's pretty universally acknowledged by gamers that Nintendo's going to need to put in a stronger showing in the online play department with its next-gen platforms. The online features of the Wii and DS just haven't been able to compete with Xbox Live or PlayStation Network. Paid DLC won't change that on its own, but it's definitely a good start.
Nintendo president Satoru Iwata confirmed at a recent investor conference that both the 3DS and Wii U platforms will allow developers to offer paid downloadable content for their games, Andriasang reports. The system is being prepped right now, and Iwata confirmed that the plan is to make those tools available to developers before the end of the year for the 3DS. The Wii U release is a bit further out, which means we can probably expect that kind of built-in support at launch.
Iwata also said that Nintendo is mostly interested in high-qualty DLC, the sort of content that adds value to a game. The company isn't interested in DLC purchases that allow players to purchase in-game boosts rather than earning them, nor does it see much value in offering free-to-play content that could potentially compete with premium titles. While Nintendo isn't likely to stop third-party publishers from offering game-boosting DLC of their own, it sounds like F2P support is a no-go.