Every single concept they hacked on to JS (immutable types, atom, declarative DSL, etc.) is a first class concept in CLJS - and it works beautifully even when building on top of their JS implementation - I feel sad they didn't just go "all in" on something like CLJS - they have more than enough resources to fix any implementation issues (ie. they have the resources to create a compiler that would generate code you would hand write with immutable.js and JSX - after all they are funding stuff like Flux and babel).
I understand why they didn't do it but it still feels so bad to see a hack in a place where a beautiful solution was just a step away.