how about turning the full circle and building a sinclair spectrum clone that fits in a pocket including battery, with a lcd lid, and of course a mini version of the classic expansion port at the rear.
ok it wont sell millions but it would be a nice tribute to a computer that taught half the world to code.
Oh ZX80 (A10 inside). Good idea but to late - Chumby creator is working on that http://www.pcworld.com/article/2020968/coming-soon-a-new-open-laptop-from-the-creator-of-chumby.html