I think Elixir works pretty well for an MMO server. I’m writing a text based MMO and have never regretted it. That’s ExVenture - https://exventure.org/ I actually don’t think I could have done this without Elixir.
I also know someone who was doing a server for an existing MMO and they were doing lots of binary pattern matching on packets which must be stupid hard on not Erlang 
The process architecture of Erlang works perfectly for a very stateful system such as an MMO. I say give it a shot!
