Also, Scala compiler slowness is virtually not a problem any more since introduction of Zinc 1.0. During development, I get repeatedly compile times around 2-5 seconds on Scala 2.11, and recent Scala 2.12.x / 2.13.x showed to be typically 30%-100% faster than 2.11.x.
Personally I rather not be in the bleeding edge and not having to deal with interop issues, or missing tooling.
Also in 2018 interop issues or missing tooling problems are long gone.
Only Scala shops can make effective use of them, and I am yet to do a project where Scala libraries were even considered.
I don’t expect higher kinded types any time soon, though.
[1]: http://openjdk.java.net/jeps/325 [2]: http://openjdk.java.net/jeps/305 [3]: http://openjdk.java.net/jeps/309