I think the issues/problems specified in the comments are not present with a Hash-only implementation. :) I would be supportive of re-considering this feature just for use with a Hash, where I believe 80% of the real-life use cases would (and do) exist. I have encountered this need before in the wild, but not with Arrays.

Write special-case classes. For example, you will have User base class with multiple error-subclasses like UserNotFound(User) and MissingUser(User). It might be used for some specific situations, like AnonymousUser in django, but it is not possible to wrap all your possible errors in special-case classes. It will require too much work from a developer. And over-complicate your domain model.

Ok, I have seen that there are lot of built-in and third party validations, but sooner or later I will face a validation rule not covered by this buffet. Can I build a custom one? Of course you can!

Library author here. I'm always fascinated by new ways people can invalidate my assumptions. I mean that in a sincerely positive way, as it results in learning.

Well. I also recall that people complained about this when I did it in redux-form, which resulted in a persistentSubmitErrors config parameter.

I'm okay with an overall design that allows people to plugin the parts they need in order to be able to generically support a compile-to-javascript language, but to bake in support for one singular solution because its popular is simply bad engineering.