Wow, great job PB.
Anyway what id like to suggest:
-Draw lines between path_track/path_corner and other entities that benefit from this in 3D view, also have a SHIFT drag feature like in H4 that makes it easier to make a path. (If this isn't there already i haven't tested Sledge myself yet)
-Basic entity info in 3D view
The other 2 might sound crazy
-A WAD editor (delete/add) on the fly .wad updating just put new textures in and have them ready to use.
-Real time .wad updating, not sure how this would work, but it would be great to edit textures in PS and have them update in Sledge instantly like in 3ds max.