I'd like to propose to add a way for a model class to provide a catch-all modifier for the case when a requested modifier isn't defined / found. Something along these lines:

class MyModel extends Model {
  ...

  static modifierNotFound(builder, modifier) {
    // Do something with the modifier and the query, and return the builder if it was
    // handled, nullish otherwise, indicating Objection should still throw an error.
    const { properties } = this.getJsonSchema()
    if (properties && modifier in properties) {
      return builder.select(modifier)
    }
  }
}

Optionally it could also just return a boolean.

I think this could open the door to many more creative uses of eager expressions and modifiers, and would be a pretty great feature that could be added with very little overhead. I'd be happy to create a PR for it.

@koskimas what do you think?