I would like Crystal to include some modern features instead just being a fast and nice language. How about stuff like: immutability, good functional programming support, complex union types, compile-time guarantees?
It also has a lightweight threading system that makes it work well as a web server. Not quite as elegant as something like Elixir, with its isolated processes, but still nice. It also supports macros, which can make the code a lot more elegant and performant compared to similar languages.