Right right right. I would add this: Ruby could well be considered "passé" someday (history tells us it necessarily will be), and the Rubyists of the future would really bristle at the suggestion that what they're doing is worth less simply because the market says it is.
The Rails MVC architecture is already past its prime, since it solves the problems of 2004. It's possible that startups may move more toward backend-as-a-service + JavaScript front-end instead of using Rails as their MVP.
In any event, the transition should be slow and I fully expect Ruby to be around for a long time, but people may notice a slow decline in demand for Rails programmers in the next few years compared to other hotter technologies. Sinatra (or some other Ruby framework) may replace Rails as a backend.
I'm a Rails programmer and I don't bristle at the suggestion that market demand changes. I welcome the change and adapt. I don't mind learning new languages.
I think that Sinatra will become increasingly popular within the Ruby community (and financial help from Heroku/Salesforce can't hurt!), but I also think it's interesting that the micro-frameworks inspired by Sinatra (Flask for Python, Express for Node, plus many others), will become the fall-back for more advanced developers because they do a lot less specification and leave a lot more space to the developer.
So I say don't give up on Ruby. And if you insist on Rails-style MVC, there's always Padrino for Sinatra, Tower for Node, etc.
