For me it would have the same things that make Typescript appealing:

- Full access to a large and mature ecosystem (one that Crystal doesn't quite have)

- The ability to gradually add typing to an existing Ruby codebase. No need to rewrite an entire application. Just gradually add types to new code and during refactors.

If I was starting a new project I would definitely be considering Crystal, but I still feel like something like this would be great. Typescript has been a godsend for my frontend development life, and I would love to have something like this for my backend Ruby development.