This Google Trends chart helps to verify that Ruby on Rails is holding it's own at least. It's important to note that PHP was omitted because it had very clearly taken a nose-dive, consistently falling for the past 5 years. Not a good sign for PHP developers. The graph is intended to compare what I believe to be the more likely candidates for future growth.
We see that Scala and Node.js are both enjoying modest success, but nowhere near the other disciplines. This makes sense given what I know about the niche functionality of these both. It seems like Node.js will continue to grow as a means of provided asynchronous connection where a real-time or "push" data flow is required. I also think it will pair well with the others. As far as Scala is concerned, this remains av very specialized form of Java that has a niche in extremely high volume sites.
There is an obvious move up for C#, which undoubtedly has links to the continued support of Microsoft .NET development in the industry. I also think that C# will enjoy some added lift from it's usefulness in Unity 3D development, though that is still very niche in and of itself.
Since I conducted this trends exploration to confirm my decision to learn Ruby, it seems only time will tell. My assumption is that the latest versions of Rails and growing body of really good documentation will support further growth in popularity. But that's an un-qualified assessment.