Siliconera found a patent application from Nintendo that is one of either two things - a new cartridge for existing DS configurations, or a new cartridge for a new DS. Or it could be both, come to think of it.

Although the DS is not named in the application, and the outline of one shown (above) is "for illustrative purposes only," Siliconera notes that the cartridge has the same number of pins as an existing DS cart.

Nintendo Patent Application Hints At New DS Cartridge Design [Siliconera]