C10k doesn't come up with Wikipedia because it doesn't do websockets. If it did it would probably have millions of concurrent connections, far over 10k. I dare say 10k is a bit passe. Whatsapp can apparently do 2m/server.
Ah, that makes sense. Still, is 2m rps within the realm of possibility for BEAM with a high-end server grade processor and heavy use of actors/concurrency?