> and will likely remain that way for a while

Not so sure, the alt-Scala train is moving fast (i.e. Dotty, Scala Meta, and Scala Native).

Scala.js is already production ready; come 2019 I'd consider present day Scala deprecated, replaced by Dotty with Scala.js and Scala Native compile targets.

In fact, initial release of the Scala to Dotty Migration Tool[1] is now available

It's happening ;-)

[1] http://scala-lang.org/blog/2016/10/24/scalafix.html