I see a lot of references to Crystal here and I would agree it is more mature but has different goals to be sure. If you want a rubyish DSL for microservices which can expose golang features and libraries then Crystal isn't a suitable match. We have to assume the later is important.

It's like saying JRuby is a suitable replacement because it's fast and has microservice libraries - it's not exactly what you want.

If the author is not planning to support rubyspec, monkey patching, runtime magic, etc. then it looks like they are closer to delivering on their objective.