I don't even think "jumping on the next new thing" is a particularly valid "career strategy". Many companies do use relatively "old" technologies and don't care

I don't even think "jumping on the next new thing" is a particularly valid "career strategy". Many companies do use relatively "old" technologies and don't care as long as the job gets done. Slack even uses PHP. Not to mention the big companies which might pay more attention to algorithm problems instead of the particular language you solve those problems in. Do the recruiters really think you are the one if your resume has all the newest hottest things written all over it? Personally I learn new technologies if they are fun to learn and make my life as a dev easier. That's it. I'm not sure if anybody jumps on wagons just for the sake of it. For example I tried out Rust, Julia and Elixir, hated the first but liked the later two. I also tried Vue a bit but with Phoenix framework a lot of things can just be done with server-side rendering so I just dropped Vue in the project and felt totally fine with it.