I think the problem is more that development has really slowed since they lost the sponsorship of the company that was funding development (which employed almost the entire dev team). It's not clear to me what the future of Groovy is. However it's about 1000x more accessible to Java developers than Scala is. Scala reinvents the whole type system and uses custom collections etc. That makes reverse interoperability (I write a class in Scala and then use it from Java) significantly more challenging than Groovy where Groovy code looks identical to native Java in most respects.
You can use Scala like that if you want to though - you can stick to the Java collections (even implement the scalaz typeclasses for them), or one effective technique is to write a Java interface and then have a Scala class implement it. Most Scala users do find it worth moving beyond Groovy-like code, but you don't have to.
> Groovy code looks identical to native Java in most respects
Maybe your definition of "most respects" doesn't include the Gradle DSL or Java 8 lambdas.
Nowadays I use Clojure for those quick'n'dirties testing Java code. A well-placed macro eliminates plenty of boiler-plate specific to the test at hand.
