First of all sorry for my poor English.
Similar proposal was written in Here but I think, I have some additional and slightly different concept for this proposal.

Just like "Camera", "Light", "Metaball", "Text" and "Greace Pencil" also Primitive objects needs their own " Class ". to have a separate Primitive Object Class than a bunch of mesh class types such as Cube, Plane, Cone, Sphere, would be really great in some different areas. We can use blank Modifiers tab field to store Primitive parameters to modify whenever it needs...

For example right now we have a Size value just in creation time for Cube, but it could be much more advanced if Cube become a Primitive object Class and all necessary parameters stores and reused later on in empty modifiers tab in properties area...

Or it could be store in Object Data Tab and Modifiers remain Clean, (thanks to my colleague to suggested that to me...) of course because of this new "Class" it needs lot of arguing for it...

It could be convert to mesh anytime you need and turn to normal mesh class or just add a "Mesh Modifier" as an upper layer to manipulate appearance of Cube and you still have your Primitive parameters to deal with. Of course Blender needs " Create mode " and a " Create tool " in toolbars to create primitives by click and drag right in viewport just like all other standard software out there.

Pros:

• In Motion Graphics it's really easy to add Driver to these parameters to have simple and fast setups
• In rough architectural modeling you will get some procedural elements to deal with later
• Everybody can script new models and add their procedural primitives to Blender just like Archipack with their customizable and procedural Doors, Windows and Stairs
• You don't have to delete and add a Primitive again if you want to change a parameter and you just accidentally grab it a little
• if " Create Mode " and " Create Tool " with drag in viewport added too, it would be really easy to add blocks of models in right size and right place, will work like a charm...
• All Ex-MAX users will be tears on their eyes

Cons:

• I couldn't find any, if so write it down.