@mark said:
I will come back to this if the popularity of using this editor warrents.
I would advocate for the built-in editor to be effective for small tweaks when prototyping (and it is already until it becomes unresponsive). There is a complication around versioning that would be better facilitated through a linked external editor. By accessing the shader code from the file and being able to save directly back to the file in the glsl folder would provide a benefit to assist versioning custom shaders.
best wishes
Russell