I have had this same idea, and thank you for creating a graphic to show it - that’s pretty much how I imagined it as well.
Also, I would love an eyeball icon by the “layer,” to hide everything with the same “layer.” That would essentially eliminate the need for a Layers Panel. There could be a Hiding Tag Manager, where people can quickly add or manage multiple names, and control color for the “color by layer” function, would have to be changed to “color by Hiding Attribute.” Perhaps “Visibility Manager” and “Color by Visibility Tag” would sound better, but “Hiding Tag” is more accurate. (Screening? Concealing? Cloaking?)
I was told that on an engineering level, there aren’t Layers anyway, Layers are just attributes of objects, like color or xyz position. This is why I tell my students to think of “Layers” as “Hiding Tags,” and to imagine, when associating an object with a Layer, that you are “tagging an item with a hiding attribute,” rather than “adding an object onto a layer.” There technically are no Layers in SketchUp, it’s just a word they used so that CAD people could find where their Layer names went.
Perhaps Outliner and “Layers” could be combined, and maybe called "Organizer?"
And then I would hope that we never, ever use the word “Layers” again in SketchUp, and retitle the hiding attribute as just that, a “hiding attribute” or “hiding tag”.