Would love an standardized ability to specify some human-readable annotation for a validation rule and then an ability to easily see this in the DETAILED or VERBOSE validation format. I.e. rather than a cryptic note that something doesn't match a `pattern: "\\S"` (best your typical library would do) I wanna say "must contain at least one non-whitespace character". And I want this standardized, so any conformant library I pick would be able to do this for me, providing a consistent experience whenever it's UI-side "on-the-fly" pre-validation or processing a submission. Unless I missed it, I think while some libraries can do this, it's not exactly standardized thing.
And maybe schema URIs weren't exactly the best idea. Not a fan how many libraries make me register a schema with some a fake URL instead of just feeding them the schema document and simply not caring where it came from at all. But since it's already there - OK, fine, it's a minor nuisance.
Otherwise, it just works.
P.S. I have no idea about the relation to OpenAPI/Swagger/RESTful APIs/whatever. I use vanilla JSON Schema as a convenient "cross-platform" DSL for JSON-serializable data structure validation, and I think it does excellent job at this. Would love to see it staying in that scope.