If a recent patent filing is any indication, Sony's not stopping with a simple motion control "wand."
The patent for "Expandable Control Device Via Hardware Attachment" points to various control schemes, including the option to join two devices together. The ability to add a second controller -- joining the DualShock with the motion controller, for instance -- is specifically hinted at.
Microphone attachments, as well as the ability to customize the controller with faceplates, are mentioned. Even crazier, check this: a "thumb reader used to validated the identity of the person holding the controller by analyzing the biometric data provided by the attachment."
While all of this sounds need, it sounds like it could get complicated and a bit messy. I already have controllers, wires, and other peripherals cluttering my entertainment center. One would have to hope that these additional devices would have uses attractive enough to warrant them finding a place in front of the television.