I can't see you up there your horse is too high. If you think that there is no place for PHP or Java or .Net in the modern web development world then you must not get out much. Rails and Node are great for some things. Smaller things. But I don't think they come anywhere close to filling all of the gaps in the web development world. Not everything is a startup and a lot of people would like to be able to work on their software 5 years down the road when node is a thing of the past.
You can support more than 250,000 concurrent connections on a node server. That doesn't seem small to me. Anything you can do on other frameworks you can do as good or better on node.js or ruby on rails.