This furthers the point. By stating a lot of companies are looking for Ruby (something that doesn't match my experience when looking) is not a testament that it is hot and in-demand, it is a testament that those roles are not being filled. Senior devs don't make senior dev money doing junior dev work. My assertion is that the majority of Rails is CRUD development that only gets difficult when you step off the golden path- ergo, those positions go unfilled and outnumber their statistical representation in what would be called 'production Rails applications'
I'm not really sure what your point about senior/junior devs or "roles are not being filled" is.
(aside: please don't delete your post and post exactly the same identical post again to clear the downvotes on it).
It's true that Twitter switch to JVM langs, but it's not true that Ruby doesn't scale (or couldn't have to Twitter's level if they'd kept it). Twitter was early days for Ruby and things have improved a lot, but the only scaling challenge with Ruby is the cost of app instances. I use Elixir/Phoenix now and run 1/4 of the app instances I used to and with much less memory required per instance. (in one app it's 1/10 the ruby instances!) It's traditionally opex cost that hurt Ruby scalability, not technical, and very few companies will ever see the level of success where the cost of servers gets prohibitively high (compared to dev dev cost).
If that's the case, then they are misguided.
> You can scale anything with enough hardware
No, some architectures or implementations can give you diminishing returns or a hard cap. Not everything can scale horizontally ad infinitum.
If you look at PostgreSQL then a lot of dev work comes from EnterpriseDB and a handful of companies too.
The thing with Rails is that it doesn't scale terrible well to "Twitter scale" (if I'm not mistaken Twitter has dropped all usage of Rails) so there aren't that many well-known companies running it, but the overwhelming majority of companies are not "Twitter scale" and it's not really an issue for them. There's a long list of smaller outfits that are not in the "top 50" using Rails quite happily.
People focus too much on "What is {Twitter,Facebook,Google,Amazon,Netflix,...} doing?" Who cares? You're never going to have the same problems they have. And whatever they are doing is not necessarily representative for the entire industry.