I was linked here, after posting thread that got closed. 
Basically, the is that editing BSP(or whatever BSP may change to) should be like using a paint brush, instead of manually placing each pixel of color at a time. There should be 2 methods of doing BSP/layouts: a large-scale mode(traditional BSP tools), and a ‘fast edit/detailing’ mode, where you can simply right-click/left-click(Minecraft-style) to add/subtract BSP detail. Ideally, the BSP would also optimize itself(to remove backfaces and similar) as you work, similar to the auto-triangulation system in Sculptris.
Bottom line: the more paintbrushes the better(and Wacom support, of course). 