If the reason people shouldn't use a tool is because they are too dumb to understand it, they're not going to be able to use the other similar tool either.
Programming in Scala and programming in Java are equally difficult. That's because the hard part is programming. The easy part is the syntax. If you are mentally capable of "getting" OOP, you are mentally capable of "getting" FP.
If a team decides that Scala is the right thing for their project, then it should be no problem transitioning the good programmers over. After all, it's just programming!
To be fair, not all people who use OO languages 'gets' it. They still get things done (there are a lot of simple things in the market) and although their works are not in the excellant range, it is good enough and they do come by much cheaper.
When resources are cheap, things get less risky in a way since people are much more easily replaceable.
Now, I do not condone or even like to work at those kind of places, but that is just the reality in most places.
A huge amount of code gets slapped together by mediocre programmers but still serves a useful business purpose. I think we should be trying to design languages that are accessible to people like that but less cumbersome to more skilled developers. Scala was intended to be such a language but I think it has unfortunately overshot its goal.
I have high hopes for Jetbrains' Kotlin project. Even though I don't do any JVM development at the moment if Kotlin turns out to be a good Android language I might pick it up just for the pleasure of programming in such a nice environment.
OOP mirrors familiar, everyday imperative concepts. FP is much more rigorously mathematical and abstract. The evidence is overwhelming at this point that the average programmer finds the former easier than the latter, despite well over a decade of denial by some of the more vociferous advocates of FP.
Those people would do well to emulate DPP's example here and recognize that the long-term success of FP depends on selling to the right audience at the right time and not promoting it as a panacea.
Programming in Scala and programming in Java are equally difficult. That's because the hard part is programming. The easy part is the syntax. If you are mentally capable of "getting" OOP, you are mentally capable of "getting" FP.
If a team decides that Scala is the right thing for their project, then it should be no problem transitioning the good programmers over. After all, it's just programming!