So I think it would be nice to have a DSL for just data validation (think jsonschema but just the bits that do with validation, no annotations and a simpler referencing system)
A DSL means that the language can be designed from the ground up for the best user experience and then compile to native languages ( the approach protobufs use for example). I don't propose any syntax or semantics that is radically different from what exists in standard programming languages today so I don't expect the learning curve to be high