I've actually seen more Scala adoption than Go. In my experience Scala is getting used in production whereas Go is something people play around with from time to time.
Because there are multiple mature web frameworks for Scala, I think. Go has yet to produce one (Revel? I think is coming close). I think web frameworks help drive adoption. I see that happening with Haskell too (as web frameworks mature more people get into it through that).
Compare Go in early 2014 to Scala early 2006, that is when they were about the same age.
If it really is set to "take over the world" it will need to be growing subtantially faster than 2006's Scala.