Interestingly, the feature they said that about (async rewriting in catch/finally blocks) is almost exactly the feature that has been floating around the clojure-sphere as an example of something tremendously complex that was made easier by being more imperative. It's hard to explain how much of a rat's nest something can be without being trapped in it yourself, but "people thought it was impossible to do _at all_, and we were doing it in a purely functional way until we refactored" sounds pretty nuts.

async in a catch/finally is exactly the feature I'm looking forward to most - specifically the ability to define what to do in a failure situation in a concise asynchronous fashion without having to fall back to callbacks or spinning up a background thread.

I would love to read a blog post about why they thought it was impossible and maybe walking through the implementation.