The author claims, in the title, that functional languages will rule, some day.
Then he does a tour describing each would-be-ruler functional language (erlang, haskell, ocaml, F#, scala) and explicitly says that all of them will remain niche languages i.e. will not rule.
His thesis is that none of the current crop of functional languages will rule, but that some new functional language not yet invented (or widely known) will.
A language can't come out of nowhere, because it won't have the critical mass of people, libraries, etc to be usable for "real work". IF a functional language is going to be mainstream in only 5 years, then there are a significant number of people using it today, and it will be generally known in the FP community.
Even F# was a) in beta for years b) solved the library problem by piggybacking on C# and c) had a critical mass of OCaml users who could jump straight into it.
The author claims, in the title, that functional languages will rule, some day.
Then he does a tour describing each would-be-ruler functional language (erlang, haskell, ocaml, F#, scala) and explicitly says that all of them will remain niche languages i.e. will not rule.