I just installed and used Measurements.jl in <10 seconds. Newish versions of Julia (1.6? the LTS?) don't distribute the package registry as a git repo.
1) It is just hard to explain this to people that work under me. 2) types in functions are no longer useful to understand the code or improve readability, since the purpose of types is only for dispatch.
I guess my dream request would be an alternative syntax for typing for concrete and abstract types. Abstract types would be used for dispatch and composibility. Concrete types should be used because the function is being specialized for that concrete type.
There's lots of nuance here though, and I've really struggled to communicate this to colleagues and peers.
I'm not sure being able to subtype concrete types will help with the specific issue you're showing here. Really the right thing to do is make the function take Numbers. If you allowed Int to be subtyped, things would still be semantically wrong, and you would have introduced a parallel inheritance tree that will break a lot of the interoperability multiple dispatch enables.