Elixir is a great fit for a game server, if you did come to find some bottlenecks there is always space to optimize performance by using a NIF (Rust with Rustler, etc), but that would only be the case if CPU bound tasks would come into play.
But to answer correctly it really depends on what you are doing on that game server, If it would be taxing on the CPU maybe a better solution could be found on a lower level language.
You can find a good discussion about the same topic here: Is Elixir suited for a performance game server?
