@Ed_ - This is currently not on our roadmap. Could you please share the use case(s) you are trying to solve?
Did you already consider using slides as a viable workaround? Basemaps - along with other scene and layer settings - are stored per slide and could help achieve the user experience you may be looking for. Another possibility would consist of adding basemap-layers to the layer stack as operational layers using Scene Viewer's Layer Manager. And then apply visibility ranges to each of them according to your needs. The majority of layers used within basemaps can be found in the Living Atlas and added to a scene from there.
