It’s far more than merely an additional ‘attribute’. You’re asking for an architectural change that affects every entity’s functionality.
- This Feature Request has to inspire a volunteer developer to invest their time to implement it.
- It’s an architectural change so they first have to propose it in the Home Assistant’s Github Architecture repository where it must be vetted by the development team. If rejected, that’s where it ends.
- If the architectural change is accepted, the volunteer developer must submit their code to Home Assistant’s Github Core repository where it will be vetted, yet again, by the development team. If rejected, they have to make the recommended revisions.
- If it all finally passes muster, it will appear in a future release of Home Assistant. Otherwise, no.
I suggest you begin exploring blueprints because this Feature Request isn’t likely to be implemented any time soon.