Also (note that I only went through the slides), it seems like he misunderstands what "All the way down" traditionally means in the context of Lisp. Clojure is different than the lisp variants that embrace this philosophy BECAUSE it's implemented on top of the JVM/CLR. You have access to the core Clojure implemented parts of the language, but you eventually hit a boundary where you explicitly cannot go further -- precisely where the Java part starts.

I guess you could argue that most Schemes / Lisps have a similar boundary, but from using both it feels different in Clojure.

In short, I think you run out of turtles to jump down onto at a certain point in Clojure.