PyClojure (in the link) didn't actually take it to the extent we are. clojure-py goes so far as to implement all the standard collections in pure python. So [1 2 3] in clojure-py is a PersistentVector not a python list.

Why? If your going to rewritte the collections, why not in Clojure? Speed?

Mostly because we have to have these collections inside the compiler. So it's a bit hard to write collections in a language that has no compiler. Chicken/egg issue..

Well now that you have a compiler you can rewrite it in clojure-py to make clojure-py-in-clojure-py :)