Racket is being rewritten on top of Chez
That discussion links to a Google Groups page where Matthew Flatt discusses the background, status and plan going forward.
First and foremost it will mean that much more of racket will be written in racket, and some in r6rs scheme.
If they can capitalize on chez's preformance that would be even better. It is really a state of the art compiler for GCd dynamic languages.