LOL at the idea that every Rails programmer will be switching to Clojure or Elixir! While they might be interesting languages (particularly Elixir) I don't see any 10x advantages their web stacks have over Rails for the typical "majestic monolith" use case. Re. EventMachine: As I understood DHH's speech, the idea is that ActionCable abstracts all the messiness around EventMachine, Websockets, Rack and threads. We won…
As a general comparison, when it comes to building server-side web apps Rails is preferable to Clojure. But for the web stacks / ecosystems as a whole Clojure wins by about 10x. The main reason for this is ClojureScript. For those who aren't familiar ClojureScript is a Clojure->Javascript compiler that lets you write your UI code in Clojure and drastically simplifies Javascript codebases. Given how much time is consumed writing UI code in modern web app development, the benefits that ClojureScript gives you over the turbolinks/js framework of your choice approach that Rails emphasizes cannot be overstated.
I've found that writing web-apps/api's in Clojure, using ClojureScript on the front-end, then using Rails to write small services where you want to take advantage of some of the great Ruby libraries is the way to go. You get the best of both worlds.