Such an editor doesn´t work, for any other real purposes.
Assigning shaders and editing their parameters is fine, but I want to add my own shaders with their own parameters, without having to extend the editor. I also want to set shader defines for shaders, which are then compiled in different versions for different purposes. I also want to use my own actions with their own settings and my own functions to move the camera as well as a terrain shader with support for 2 textures and one blending 16 textures together with and without normalmap and the required painting tools. I also want to adjust my own global variables and not some predefined ones. Painting and moving objects, as well as painting a terrain texture with 4 textures is something I can code in a day or two, but making it flexible would probably take me weeks.