Um, I think you might be over-attributing language features to project failure, there. The language subsetting issue is a huge problem, c.f. C++. The complexit

Um, I think you might be over-attributing language features to project failure, there. The language subsetting issue is a huge problem, c.f. C++. The complexity of Scala makes it very difficult to understand a lot of library code, even if you're quite competent in it. To keep code for a large code base manageable and understandable, most companies will end up defining the "allowed Scala" in a coding standard. This is a failure of the language, IMO.