Given the nearly unanimous recommendation that all geometry be kept on Layer0, and the strange problems that result when geometry is moved to other layers, I question the ease of changing the active layer - it’s just too easy for newbies to change.
In my own use of SketchUp, I’ve yet to find a reasonable use case to move anything (actual geometry, labels, dimensions, guide lines, etc.) other than groups and components off Layer0, hence if it were up to me, I’d simply remove the ability to change the active layer!
However, in order to maintain backward compatibility, simply making it very hard to change would work. Here’s just one way I thought of:
Make the appearance of the “Active Layer” selection in the Layers panel controllable through the “Window->Model Information” choices. Specifically, default it to “Not Visible” and let people who really need it (very few, I’ll bet) set it to “Visible”.
Addition March 7: I changed my mind slightly! Control should be in “Preferences”, not “Model Information”: