Posted to Clojure Google Group, but it's not showing up there (https://groups.google.com/forum/#!topic/clojure/GITSKLmFM60), so...
In an effort to simplify the implementation and improve the RxJava experience for all JVM-based languages, we'll be dropping direct IFn support (and Groovy closure, Ruby proc, etc) in the next release. Instead, for each supported language (Scala, Groovy, and Clojure at the moment), we'll be providing a set of utility functions/macros/implicits to assist with interop. In the Clojure case, this will consist of a namespace, probably rx.lang.clojure, with the following helpers: