This has been planned from the beginning. It’s why we have the Add Cube tool in Edit Mode, which is supposed to be the beginning of it. For some reason, Campbell stopped working on it, and so it has been left in this half finished state since the Code Quest ended.
I hope that either he or someone else steps up to finish it.
https://developer.blender.org/T57210
Blender really needs a developer who focuses mainly on these sorts of things: Maybe the Qblocker guy could contribute to help developing this further.