It always surprises me to see these sorts of projects NOT based on Racket. I guess that is the danger of Scheme, it's so easy to reimplement the base language that everyone is doomed to spending lifetimes reimplementing the standard libraries.
The "designed to be hosted" structure of Clojure points the way to how this could be approached. Stallman's designs for Scheme and GUILE are along these lines as well.
If you are going to build a Lisp processor, then you probably don't want a Lisp compiler or interpreter in the traditional sense, which is what Racket gives you. Maybe what you want is an interpreter in hardware.