Why use Rails as a frontend? One of the reasons I'm using Go for service decoupling is to get rid of Rails long startup times. I just route the requests using Nginx and skip Rails altogether.
I think jlhonora just means to proxy from nginx directly for the services that aren't powered by rails. Like 90% of the site served from rails and the high performance services are just different nginx backends.
This is what we've done. Start with Rails behind nginx, add varnish caching when needed, redis when needed, node (or golang or w/e) when necessary for the real time bits, etc.
Get's a bit messy with all these moving parts, but I think that's the just the nature of large projects. Elixir + Phoenix looks interesting though...