I could build a 3D printed prototype for something like that from Shapeways (do the 3D model and submit it), but it would probably be a couple hundred dollars and a LOT of work, then you'd need to sell the idea to a company that specializes in making cases....
As far as the overall idea goes, it would be pretty simple to measure the contours and design the shell case, the top would fit the Xoom, the bottom could hold a keyboard... Then you'd need to make a way for it to stand up (the ASUS keyboard has a giant battery to counter balance the top tablet) But again, with making prototypes, it would be a lot of work and would be pretty cumbersome... And not to mention expensive.
I made a small protective case for Dextro energy tablets (I'm a type-1 diabetic, the dexto sugar tablet packge is maybe 5/8th of an inch tall, 1-1/4 inch wide and 4 inches long), fairly simple piano hinge and a latch, and both pieces were about 60 bucks together. So for something as large as a Xoom with a bottom case big enough to support the Xoom AND hold a keyboard, a prototype could easily reach 2-300 dollars, and without a case company jumping at that opportunity, I wouldn't put up that kinda money....