That's kind of a straw-man argument, isn't it? Nobody is moving from high-level languages back to C or even Java. The talk here is of moving from "early adopter" to "innovator" on the adoption curve. And I'm just making the point that when you do that, you necessarily either contract your candidate pool, or add ramp-up overhead to new hires.
I'm defending their choice to move to Scala (a "niche" language) after running into performance problems with Ruby. I don't think it's a straw man to mention Java and C++ as representative of the non-niche languages that perform significantly better than Ruby. There are plenty of faster language platforms they can move to, but which ones offer a powerful and elegant language? As far as I know, you either pick a "niche" language that few developers know or you pick an old and clunky language like Java or C++. In this case, you have to weigh the ability to hire new people, which would be better for the more popular languages, against the ability to retain your existing Ruby developers, which is better with an elegant, powerful language.
