The way I see it, 2D is inherently included in 3D CAD, but 2D CAD is limited it's 2D-only nature.
Parts physically exist in 3D CAD. When you're working on your blueprint, it's done more-or-less by performing the operations on the part that will be performed when it's manufactured. Every 2D view you could ever want is inherently included in a 3D part.
But 2D... it's not much better than sketching by hand on a piece of paper. Everything's disconnected. You can forget to add a feature to a view, you can make mistakes between views. With 3D if you add a new flange or a hole or whatever to a part, every drawing is instantly updated.
At least, that’s how I view 3d.
At the very least, the tool should be able to do additive and subtractive operations (boolean). Union, add, subtract, intersect, etc.