I've been wondering the same thing. It strikes me that this is mainly a 2D notation used in ortho views, hence more appropriate for Layout than Sketchup. If someone has a good (existing, not created just for this topic) 3D use case please present it.
Also the main users would be architects, engineers, etc. using Sketchup commercially so having it in Pro only would be appropriate. But until the Layout API is completed it won't be possible to do it as a Layout extension.