A few days ago, we finally merged an early implementation of link layers (layers linking to external files) into @npub1jxdd...txs3.
This has various usages, e.g. the ability to work at several people on a same image by linking a separate document (e.g. someone working on backgrounds and another on characters). Or again when working with different software.
For instance, in this example, the layer links a #SVG file. As soon as it is saved in #Inkscape, #GIMP picks up the updated version automatically:
