Excellent idea -- thank you! Seems to be working in SU 2019, although I haven't tested extensively.

Also, thanks for sharing the raw RB file, which is nicely commented. I'm looking at it trying to figure out how to make a version that turns ON a layer in all scenes (maybe I could just cut/paste-in-place the layer's contents). I'm quite new to Ruby, and this looks like a nice script to play with.

Users, note that you must set the target Layer as active -- not just highlight it. Also, using undo doesn't undo the TOLIAS operation -- I suppose because it only undoes the Layers operations, one per undo, without updating each scene again. This is typical SketchUp behavior -- undo doesn't undo Scene updates, unfortunately.