This is a feature request that is about reusing parts (layers and materials) of a project file in various ways.
First off, layers within an SSA file: I'd like to be able to duplicate a layer such that I can easily create layers with variations. Also, if I have multiple materials in a project file, I want to be able to copy one or more layers to a different existing material or to a new one.
In addition to the above, I'd like to be able to copy materials and their layers via exporting a Material as a SSA file to a SSA file of its own, and then be able to import it back in to a new file. Or better yet, be able to import via selecting an existing SSA file and then get a dropdown (or with tick boxes) of materials in it that I can choose to import. Both ways can be useful, especially when a SSA file is getting huge. Other export options means losing the layer properties.