At any large scale what becomes more important is fault tolerance. Even though Go has goroutines and sane and modern concurrent IO handling, goroutines still share memory. So then even a super fast 1M req/s system is no good if it is down 50% of the time because it crashed.
Also theres a good writeup on how Erlang was used for some of Call of Duty's infrastructure. http://www.erlang-factory.com/upload/presentations/395/Erlan...
Sounds like you're already committed to Go, but just wanted to make the case. Concurrent, fault-tolerant, highly scalable systems is Elixir's sweet spot.
[edit] One more, great talk from the Elixir Conf on how Martin Shurrer used Erlang to build a multiplayer card game. This one is particularly good because it deals with scaling, game states, and is very practical: http://confreaks.tv/videos/elixirconf2014-otp-in-production-...
Go was familiar from the jump, and easy to reason around coming from primarily Objective-C, C, Python, and C#. Considering timeline, it wouldn't have made sense to be so behind the learning curve.
With more time or breathing room, I think Erlang would be a space I'd jump into with both feet.
Edit: I know Martin through common colleagues and have worked with him in Austria. He's a great dev, and that was a good watch. Thanks for the link.
I liked Elixir a lot too, but when trying to pick the right tool, the learning required around Elixir/Erlang, the VM, and OTP didn't make sense when writing a production system that needs to handle 1000 req/s or more with a small staff. Go handles what we do fantastically.
Now you know someone. :)