> The sad fact is that these people have not been aware of the realities of the industry they have been working in. Their job and their job security is no longer secure. Never let this become you!
It sounds like the author values language/framework knowledge above expertise. Speaking as a backend dev I find as you move up in seniority it becomes impossible to keep up with the latest technologies. Learning management skills, being move involved in architecting and business development all take time. You may end up doing code reviews, project management and cleaning up the 'legacy' (read broken) parts of the system. Does that make you less valuable?
To a company that insists on every part of their project being built in the latest cool language/framework (and yes, I still class NodeJS as this) then yes. To a pragmatic company, which may choose NodeJS if it's the best fit, or Rails, or PHP, or Java - no.
We're back at the skills vs language debate, one which I thought has been done to death.