It would be nice if there were default implementations on all the IPropertyCallbacks so that a user would only have to override the methods they really wanted to rather than all of them.

Stale issue message

This is useful, but what I mean is that if you do something like

public interface IIntegration {

    default void mod_init() {
    }

    default void crafting_register(RegistryEvent.Register<IRecipe> event) {
    }
}

You can simplify your entire API and make it more legible

See the class WeaponPropertyWithCallback in the api.weaponproperty package. What you want is there.