This is a very neat little project. If it were scaled up to something the size of a Tandy 100, it could be a serious little hacking machine. I've considered such a project, but it's rather tough to find any SBC of appropriate capacity (in terms of CPU and RAM) that is stable (i.e. not a Raspberry Pi).

However, uLisp is really only usable for limited use-cases (i.e. whatever you'd use a microcontroller for). A full implementation of Common Lisp and at least 256MG of RAM would make a Lisp-device a formidable mobile device.