Scala has achieved critical mass, it has shown steady growth over the years and will likely continue. It is entirely possible it will never become as big as Java but that should not be the requirement, it is plenty big enough you can count on it.
I have been developing large scale projects in Scala for the last 6 years and I can't imagine going back to Java now. Scala makes it easy and fun to write good correct code.
Scala is boilerplate free, it feels a bit like your favorite scripting languages yet with compile safety a powerful type system and lot's of help from IDE.
Obviously Scala supports Functional Programming which is essential as everything becomes multi threaded and/or distributed. Scala makes it easy to write functional code and is immutable by default, yet it isn't opinionated and you can use other paradigms when they make things easier/faster.
It's fun to write, you don't have to be a genius to use it, though with weak members on your team you will want a strict style guide. I found using Scala is a selling point when recruiting top talent, even those who never used it. Those who have used it, especially coming from a Java background are instantly hooked.
This was verified again in recent Stack Overflow developer surveys where Scala came out to be a very loved language, nearly everyone who tries it falls in love.
I highly recommend