Hmm well neither exactly. At the moment it’s not creating any new type of image format, although I do want to implement an open raster importer/exporter so that it can be saved and imported to krita for example.
And it’s also not just a fancier way to access the texture paint slots (even though it does access them). Afaik the texture painting slots are only a way to access which image is currently being drawn on, but has no power to influence the draw order, opacity, blend type, or anything else, because this power is reserved for the material/nodes system. This addon creates the proper node setups to correspond with how layers are manipulated in the layer panel, as well as selecting the proper texture slot so that you’re actually painting on the correct image. I agree though that it’s limiting not being able to save to a file containing the layers but this is part of the future plan.