It's not dead yet. David Miller has been untiringly maintaing Clojure's CLR implementation for years now. Clojure CLR right now has feature parity with Clojure JVM. core.async is still alpha (it's also an external lib), I bet that once it reaches some stability David will add support for CLR in a weekend (as it has been usually). Unfortunately that doesn't mean there is much community interest in the CLR port though, but David's relentless stewardship of the project is relentless.

Example: https://groups.google.com/forum/#!topic/clojure/Kvefcae2W6s

Project Source: https://github.com/clojure/clojure-clr