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.
I had second thoughts about the Pi Zero when I realised it had no audio onboard (except via HDMI) and also web browsing was quite painfully slow. I'm not sure yet what SBC (single board computer) to use in its place, I think a Raspberry Pi 3 with the RJ45 and USB ports removed would work but I am also considering the Lemaker Guitar https://www.amazon.co.uk/dp/B01C4JOJ8S/ref=cm_sw_r_sms_awdb_bYj6ybANEW8ZX - this has built in support for charging and running from a LiPo battery and a swappable module with the CPU and RAM on, making it upgradable.
I have successfully butchered one of those cheap tablet keyboard cases as I previously mentioned, this yielded a keyboard with a thin metal backplate and a small controller board with the USB cable attached. Dimensions of the keyboard are approx. 205mm x 82mm x 5mm (8.1" x 3.2" x 0.2". Key feel is not as nice as the Jornadas and certainly not a Mobilepro 900 but easily beats a touchscreen keyboard for me. Keys are scissor switches (like a laptop / HPC keyboard) so not too wobbly and with a nice soft 'click'. Pics to follow..
Progress is likely to be fairly slow as I have an upcoming summer project (building a new garden shed / workshop) but I am determined to get this done in some fashion.