While Clojure has failed to become mainstream so far, it certainly hasn't failed to be influential. Whatever programmers use in a generation, it may have a lot of ideas from Clojure in it!
And while it's far from mainstream, it's certainly a healthy language with a vibrant community nowadays. There's also a lot of exciting work being done on ClojureScript, and I think that it has even higher value proposition seeing how front-end development with Js is a hot mess right now.