Hirokazu Hamamura, the head of gigantic Japanese gaming mag Famitsu's parent company, made a prediction that Nintendo will unveil the next-generation DS at E3 2008 this summer. Normally we wouldn't think anything of some businessman making predictions, but if anyone knows what's going on with Nintendo, it's Famitsu (the gaming industry and gaming press are really tight over there).
Kotaku says it took two years between the transition from DS to DS Lite, so a summer DS Lite to DS EXTREME transition might be possible. Our prediction is that they'll do away with the GBA port altogether, saving space and hardware costs.