Ultimately you are in a better position to judge what your audience would find relevant and what kind of focus, functional vs concurrent programming is needed.
Often workshops focus on highlighting on the shift in thinking between object-oriented, functional and concurrent approaches.
Two years ago there was a discussion about implementing Tic-Tac-Toe in Elixir.
Torben Hoffmann use the Game of Life to demonstrate concurrent thinking (and there is also Implementing the Logic for a Board Game in Elixir).
