According to DSCentral, Firaxis designer Sid Meier answered a question on the company's website relating to potential Nintendo DS development.
Question: Do you have any plans to develop for the Nintendo DS? Firaxis' strategy games are a natural match for the dual screen, touchscreen enabled handheld. Other strategy games such as Europe Universalis II, Age of Empires, and Command and Conquer have been announced. Civilization and/or Alpha Centuari would fit in nice.
Sid: It's certainly something we're exploring. Our goal is to make great games and deliver them to players on whatever platforms make sense for the game. I agree that the Nintendo DS would be a good match for some of our titles - so stay tuned for more info. soon!