I cant help but think of Jane Street Capital's use of OCaml when reading that line. From what I understand there are some extremely bright people writing fantastic code over there.
In my project different source files using different libraries could almost look like different languages due to the DSLs of the libraries those source files used. Maybe it's just my lack of experience with Scala, but I dislied this because I thought it reduced readability.
Even worse is when two or more DSLs in use in the same source file conflict, for example, with their implicits. Then you may be stuck with different source files using the same library but with different syntax, one with the DSL syntax (where there were no conflicts) and one without.
I suppose this is something you get used to with Scala, but I wonder if you've run into this and if so, what your reaction to it is?
On the other hand, the compiler is extraordinarily slow.
Generally Scala appears to use less time, less memory and less code. I have not ever used either so I cannot anecdotally confirm this.
(Though I suppose that is like saying you should only look for your lost keys under a street lamp)
The other JVM languages reduce some of its flaws. Go, I have found, avoids them all.
So, yeah, I would be curious on how to support either hypothesis, as well. Best I could think would be to track job listings. While I think you will get a few folks doing things for the novelty and to make it work. I think the majority entering an industry are chasing the buck the last success made.