This is a bit of a contentious post (that commit is comedy gold) but I think people talking about rails using coffeescript as the new default client-side language are missing the point that coffeescript doesn’t complement rails, it supersedes it.
I come from a biased position, since I’m known for front end development, but I’ve been doing rails since version 0.6, and most of my contract gigs have a ruby on rails component. Rails is a great tool for building middleware, and when it was invented it was a perfect solution.
Common technology was MySQL and PHP. Front end development was pretty low-impact, mostly you generated html on the server and sent it to the client, sometimes you sent html fragment back and forth for some ajax-interactivity.
Into this environment, rails was amazing. It was a great framework for building apps, gave you conventions on how to structure your app, forms and data models. And then rails came out with the ajax helpers and people went crazy for it. Over time rails added excellent json support and people started using it to create pure json api sites (like twitter does these days), but fastforward to 2011
Rails doesn’t need to feature in any of this. And although rails will live on forever (like php does), and it’ll probably adapt to it’s new role as an authentication and permissions layer between the client and the database, I would be surprised if a better solution doesn’t come along. It could be a more mature CouchDB authentication / permissioning framework, or Postgres might release a json interface and people go back to writing stored procedures to authenticate / secure requests.
Middleware is becoming less important
Note that I’m not saying node.js is going to replace rails. I think there’s less need for middleware these days.