The big breakthrough is making it easy to create new DSLs for any situation. Every area of the OS has its own language (and you can just add more if you feel the need) so that the whole OS including networking and GUI is very compact, understandable, and hackable. This particular project focused on compactness, just to prove that it is quantitatively more expressive.
I was studying Racket lately, and it sounds very familiar now. DSLs, or dialects as Racket calls them, is surely way to go and improve productivity, it should however, always be possible to descent down, or escape from that DSL, where needed, to avoid the hacks that work around a certain limitation of this or that DSL. (lisp macros, wink wink)
