I welcome you to start your next hot startup in 2017 using Swing/Java instead of React/React Native/Node/Ruby/Python/Go/Rust/C++ etc. The merits of the stack are determined by both intrinsic factors and the market. Ignoring the market (remember Palantir is hiring in SV / Palo Alto) you risk alienating potential hires and current employees. [1] Another great example is EHR/EMR market with Mumps etc.
If your problems are interesting and we get along well, I will happily work on whatever out-of-fashion tech stack you have that the web development intelligentsia sneer at. And we'll do great things!
I had a blast making Wordpress development not suck and it led me down a lot of interesting roads and brand new ideas.
These other potential hires who only believe in The One True Stack are silly.
Java is still the language of choice for many new projects at Google. Your options for new large server-side projects are, realistically, C++, Go, and Java, arranged in order of how high-level the language is. Java is a perfectly rational choice even today given those options.
Yes, they use it at Google and basically everywhere else. The JS circle jerk is extreme here. JS has its uses - mostly because it is the default language of the web and the web has many uses. That is all.
But I really resent this sort of mentality. It causes a lot of work trying to 'upgrade' your tech stack when you'd get more benefit from fixing your architecture, refactoring, building new features, fixing bugs etc. I'd rather work on improving software in meaningful ways and make the company more money.
[1] https://www.quora.com/Why-does-Palantir-use-Java