Since this great little piece of hardware can support a BASIC interpreter and a Lua interpreter, how hard would it be to get a LISP interpreter working? There is already an ESP LISP project:
In the words of @uli , "I've never done anything like this before", but as a fan of LISP, this could be really fun. Basically a LISP implementation that has the same access to the hardware as the BASIC interpreter. I'm not really sure where to start, but would be willing to explore the idea with a few pointers.