I actually spent a part of the weekend re-evaluating Scala build tools for the who-knows-how-many times now.
Gradle did come up and I was astonished to discover Groovy is now over its performance problems and may very well be a worthy platform to develop web services on!. Only if Groovy had a clear road map and profound backing it would have been the true "Scala killer".
I think it's worth giving Groovy a second chance by its own, and I've set up some time to do that.
And lastly - after looking at gradle as a build tool for Scala - it looks OK, however I don't think I will ever withstand all of the hate and incompatibility from the Scala community because I've deviated from SBT (which is another problem by itself).
> I was astonished to discover Groovy is now over its performance problems
It isn't. Gradle still ships with the slower Groovy 1.x, and Grails, altho it ships with Groovy 2.x, doesn't actually use any of the faster static-typing, presumably because it's still too buggy.
It would be nice if Gradle used Scala or Kotlin as its build language instead, but with a name like "GradleWare", I suspect someone from VMWare is pulling the strings to keep Gradle tied to Grails (and Groovy).