> LOL at the idea that every Rails programmer will be switching to Clojure or Elixir!

I meant those as examples based on what I see around me. That's exactly my agony, I don't know what is next and, if I did, I would be learning it already. At this point, I just feel it is not Rails.

> Re. EventMachine: As I understood DHH's speech, the idea is that ActionCable abstracts all the messiness around EventMachine, Websockets, Rack and threads

If you are using Event Machine you can't abstract away from it. You need to do all I/O using Event Machine aware mechanisms. You can get rid of callbacks by using fibers but you are still required to use an API specific to Event Machine. For example, you can't use File.read to read a file as that will block your event loop.