[lmm]

To my mind the bandwagon has been and gone, with those companies moving away from Scala being those who arrived on the bandwagon and departed with it. But I guess it looks different from the inside.

If you're treating Scala as "just a better Java" then you're not writing inefficient code; you're writing code that could be better Scala code but is still better than the Java you would otherwise have written. Even if you never move beyond the "Java without semicolons" stage, hey, it saved you writing all those semicolons.

But Scala absolutely is a full language and not just a better Java; Java 8 barely scratches the surface of what you can do in Scala. I don't think I could bear to work in a language without higher-kinded types again.

Kafka has some very particular constraints that I don't think apply in general; remember they're making a framework rather than an application.