How cozy is the Microsoft-Nintendo DS relationship? Just cozy enough, apparently, as Phil Spencer, general manager at Microsoft Game Studios, points to Nintendo's dual-screened portable as a training ground of sorts for its own service, Xbox Live Arcade. He tells Develop that having a developer like Rare focus on DS games is "important for us to build that experience as a publisher and game developer and understand what it means to build lightweight, maybe shorter session experiences, and maintain that design innovation."
With a Nintendo DS version of Rare's Viva Pinata in the works, it would seem that Microsoft might also see an opportunity for cross promotion, courtesy of the DS's massive userbase. That's something clearly not needed for, say, Halo.
Spencer points to software for the Nintendo DS representing what "state of the art game design might be in future" and hints at nurturing further development on the platform. Let's just hope that doesn't somehow mutate into a flood of brain training games arriving on Xbox Live.