Crystal seems like a great high-level language and alternative to Ruby, but the biggest blocker for me using it more generally is the lack of multi-threading support. There is WIP support for threading but it has not been committed. Moreover the Crystal developers either don't do a great job of updating their multi-threading roadmap [0] or work on multi-threading has died off. (I assume it is the latter because the thread-support branch has not gotten any commits in 10 months [1].) Ultimately if I wanted the high-level aspects of Ruby or Python and wanted more performance and great thread support I'd probably go with Elixir (even taking into consideration BEAM weirdness).
[0] https://github.com/crystal-lang/crystal/wiki/Threads-support
[1] https://github.com/crystal-lang/crystal/tree/thread-support