I would not mind more media capabilities in the DS. While already a great system with many owners, adding some media features such as music playback would be pretty neat to have. The DS would also need a harddrive for it though, or it could be an external harddrive made by Nintendo.

With a harddrive, Nintendo could also allow developers to make DLC for the games produced on the system. This would add more replayablility in the game and Nintendo would make some more cash on the side. The content could also be themed backgrounds for your DS or a new interface. Video playback would be nice, but I think the dual screens would be an issue with watching a movie.

With the DS, Nintendo has many ideas they could do with it and greatly profit from the ideas also. If they listen to the ideas of the gamers who own a DS, they could rake in some serious cash.