Here's an example of what a quick draw function would be like. Kinda like Skecthup but applicable to Hammer.
SploinkThis is from 3DS Max of course. The reason Max is #1 when it comes to architectural construction in 3D is because of some of its clever geometric tools. How is that any different from mapping really? If sledge could draft better than the average hammer, it would be better and people could use its power to make mapping more enjoyable rather than having to man-handle so much stuff. I think we should look at what other programs are doing right. Not just level editors, but big modeling and drafting programs.
I was also looking at spline drafting, but that's probably too much for now. I also noticed moving a transformation origin is useful, and having it snap to the grid. Another is different kinds of snaps, like to midpoints, centers, vertexes, and intersections of faces. For some reason, this is always a key element in basic drafting in CAD.
Oh... A grease pencil is mandatory if you make this able to be networked for live co-op mapping. Wasn't that a thing a while back? Sledge multiplayer? Anyway, the ability to show with sketches would be key to communication. Food for thought.