In the linked post, author Duncan McGreggor estimates only 10-20% of US tech companies have major investments in Functional Programming. Notable abstainer: Google. Why?
New programmers with little experience to defend find it easier to learn new methodologies. Senior engineers will pick up new tech, like Functional Programming, if they're 1) research/academic oriented, 2) easily bored, or 3) have little competitive drive. FP seems to be most adopted by smaller companies, because it's easier to hire/train up a critical mass of experts in the subject.
I've typed "Functional Programming and other new technologies", although FP is as old as Lisp -- 1950s! There are theories why Lisp didn't take over the world, but that's another blog post.
Electric Duncan: The Future of Programming - Adopting The Functional Paradigm?
Electric Duncan: The Future of Programming - Adopting The Functional Paradigm?