What semantics is crystal lacking? Obviously it's not a 1:1 replacement as the ecosystem is different, gem management (shards) is different, etc. Crystal also has union types and concurrency.
For people who want a syntax like ruby + performance/concurrency, but are willing to deal with a different ecosystem and having to do more stuff by hand, Crystal is a nice choice.
For people who want a syntax like ruby + performance/concurrency, but are willing to deal with a different ecosystem and having to do more stuff by hand, Crystal is a nice choice.