I mean if the editor offers primitives and even vertices, faces and edges manipulation what on earth it would take to give basic operation like bending or drawing with pencil and extrude which would be very productive for level designer. Level design must be production not non productive like having 2 or 3 programs running on the computer and going from one to another just to make a level. Think about it.
With the very talented programmers at Epic, it would be painless to add this feature in the 2D views so we can draw a form, and having Bezier lines with how many vertices we want for smoothing and once the form is completed a simple function to extrude it and voila we have a geometry with very little effort and we can do a lot more as a level designer. From what I saw with lots of other editors this kind of small feature is there. UE4 Editor needs it !