It's pretty obvious that they are in a better position now to build a highly realistic prototype. The Model S prototype was built on top of another manufacturer's frame; it only looked like a Model S. The Model X prototype is derived directly from Model S. So it could be extremely close to the production design.
Exactly I imagine the Model X is mechanically a Model S with a lift kit and a Full wagon body. I imagine the finished product will have AWD (probably as an option, maybe with a Sport package), but I bet the prototype is RWD.
Will Model X have the same chassis as Model S or is it going to be completely different aluminum body panels? I mean something like Audi AllRoad being the same as Audi A6 Avant with different plastic parts, Quattro and more ride-hight?
Based on the 'skateboard' platform I see the car as a unibody/body bolted to the battery chassis. I imagine that it is a new body, and body panels to make it truck like on top of a lifted skateboard. And possibly AWD for the demo, and certainly for the production model (probably as part of a performance/sport option). EDIT: I mean to say that is the concept. I am fully aware there are lots of complications, and details that make this much easier said than done.