>one of the reasons we could not switch to Scala was the steep learning curve which would be a big problem for new developers joining us

I think this is overblown. Yes, the language has a deep learning curve, but you're really trading off language complexity for lack of framework complexity. Because the language is so powerful, you'll see a lot less 'magic' frameworks (no need for a DI framework, no need for AOP, etc) so applications tend to have a really low barrier of entry to work with. We hire new developers all the time and they are productive way before they master the language.