Always Innovating's Touch Book is probably close to what you want. The hardware specs are open, there are pins for serial on the board, and it can run a variety of ARM based Linux distros (Android, Ubuntu, etc).:
http://www.alwaysinnovating.com/touchbook/
That looks very nice, except for the abysmal 1024x600 resolution. I'll give Apple credit for having the iPad resist the inexplicable war on vertical pixels.
Plus the disassembly instructions are provided by the manufacturer: http://www.alwaysinnovating.com/wiki/index.php/Top_part