I think the real key is to accept that with well-defined interfaces, polyglot environments really do have an advantage, because different languages really do ha

I think the real key is to accept that with well-defined interfaces, polyglot environments really do have an advantage, because different languages really do have sweet spots. And fortunately, POSIX gives us those well-defined interfaces. POSIX process boundaries, pipes and Unix & TCP sockets are excellent interfaces to separate tools written in different languages. A well-written RESTful service listening on a Unix socket can work wonders. If one's using POSIX, then one's team can work on each tool in the language which best suits it and in which the primary lead is most product. If someone moves on, then the rest of the team can support it because a) good programmers can pick up good languages quickly (I don't want to hire or work with mediocre programmers) and b) each service is small enough that anyone can understand what it does by looking at a small amount of code.