The Metroid Prime: Pinball demo at E3 confirmed speculation about an external rumble pak for the DS. When booted, the game displayed a “GBA Option Pak” message, meaning that the rumble pak fit into the GBA slot; and presumably, the ambiguous nature of “option pak” likely means that Nintendo will introduce more than just a rumble add-on, presumably.
But will the rumble feature be a standard with all (or most) DS games in the future? Will it be sold separately? Or come packaged with Metroid Pinball (and possibly other titles) like the original rumble pak was with Starfox 64 back in the day? We’ll keep you posted.