Maybe a way to add layers to Shmeppy that could feel more approachable would be to add them not as full-map layers, but as their own distinct objects.
I think they’d feel a bit like platforms or windows. So you’d create a window of some size and could move it around. Within the window you could draw/do anything you could do normally. But you can drag the window around, hide it, and change the opacity of the entire window.
I could imagine people using this for a variety of purposes. It seems pretty flexible. And I think users would be much less likely to accidentally edit a window/layer they didn’t intend to write to (which is one of my major concerns with full-map layers).