Add model support for POROs to Rails core? (like ActiveAttr or Virtus)

I imagine this has been brought up before, but I’d really like Rails
core
to add a library which allows plain old Ruby objects (POROs) to be
treated
as models, such as ActiveAttr (GitHub - cgriego/active_attr: What ActiveModel left out)
or Virtus (GitHub - solnic/virtus: [DISCONTINUED ] Attributes on Steroids for Plain Old Ruby Objects).

ActiveModel comes close to doing this, but there are quite a few gaps
such
as the ability to define attributes on models, e.g.:

class Person
include ActiveAttr::Attributes

attribute :first_name, default: “Bob”
attribute :last_name, type: String # type-casting
end

The main advantage I see in doing this is that developers no longer need
to
rely on a third-party library which may diverge from Rails standards.
Moreover, there may be opportunity to consolidate functionality common
to
Mongoid and ActiveRecord in this library.

Thoughts?