I've just bought a Pi Zero W, tiny USB hub and a 5" touchscreen (resistive) with the intention of building a HPC format device. Thinking of one of those USB tablet keyboards that connect by USB to keep things simple, I think the keyboard will be about 20 x 10 cm so would make it more Mobilepro sized (albeit with an undersized screen). My idea with the case is to machine and assemble one out of Acetal or similar engineering plastic (thankfully I have access to a tiny milling machine).
Hard bits will be the hinges and passing HDMI and USB cables through them.
It's encouraging to know I'm not the only one contemplating something like this!
I could put an Ipaq HX4700 in the lid part with an USB keyboard below...CE6 handheld in 30 seconds!
Also, don't know how many of you have ever built a remote controlled airplane, but Monocote, Coverite, Skintex are all plastic based sheets of heat shrink material. I could cover that wooden form and using both a hair dryer and heat iron, it would adhere to the wood like it was glued on making it really coverful and shiney and smoooooooooth...as if it were molded out of plastic.