I don't know if I'd move a project without scalability issues (and that's an important caveat) to Elixir purely based on the language facilities like pattern matching, but I'd definitely start one with it. Pattern matching alone is something I feel the lack of every time I get into a Ruby project these days.

For a project where scalability is a concern, I'd have no qualms about moving it over. At the very least I'd carve out the slices which most impact performance and implement them in Elixir and deal with the PITA of having two app servers. In a real world project with these kinds of issues I've seen some pretty huge improvements by doing this piece by piece.