> Erlang generated a lot of buzz several years ago but aside from the recent success of WhatsApp it never quite stuck.

Erlang is quietly running a lot of stuff out there. It's almost certainly running some bits of infrastructure that you use daily, or in a supporting role for it. People who are not old Erlang hackers are picking it for new projects.

Erlang hasn't been and probably will never be quite mainstream, but to say it "hasn't stuck" might be missing the point: it's a mature and performant language that has some very nice standard features in OTP that are lacking or less mature in other languages. If your problem domain is smack in the middle of Erlang's strong points then it's worth considering. It's not going away any time soon.