Managing documents with background images and text boxes is hard -- selecting the correct object is challenging. Introducing lockable layers, similar to Draw already supports, would make this much easier.
Specific use case: A4 page with a full background image (zero margin) and text boxes in the foreground of the page with solid colour background. Selecting text for editing, instead of selecting text box or background image, requires many clicks and sometimes workarounds.
Agreed, setting to NEW.
Layer in the sense of ODF are not possible for Writer or Calc, but only for Draw and Impress. Nevertheless it is valid request for better object handling in the UI, but it is not related to file format (ODF layer).