An interesting example is the addition of `{-# LANGUAGE LinearTypes #-}` to GHC. The primary interest for this "experiment" is not from academia but from industry (tweag IO). Another example is `QuantifiedConstraints` which was quickly caught up by practical applications as well. Haskell is not just for academia, it is very much intended for practical use after all.
It is intended by it's creators as a research language. That doesn't mean it isn't suitable for practical use, it just means that you should expect it to continue to gain features and grow in complexity.
It's not C++'s goal either, AFAIK, but major new features keep getting added to the language anyway.