Thanks for expanding. It sounds like the main problem with non-mainstream languages is the difficulty of recruiting developers who know the language well enough (rather than some technical quality of a language like Clojure that makes code hard to maintain) . That is a pretty uncontroversial statement and is probably very true. The pool of Clojure developers is probably quite small at the present moment in time.

Would you regard the use of a non-mainstream language to be, in of itself, technical debt?