An excellent point. Definitely something we should all keep in mind when promoting cutting edge tech choices.
That said, I don't think the matter is quite that straightforward where I come from; I would imagine Clojure dev head count in the whole of Finland is in the low double digits. If I were making business decisions involving future staffing, I would not feel confident I could replace the (hypothetical) only in-house Clojure dev in this job market.