Comment 10 for bug 578741

PSD: Already can be embedded or linked in Scribus, so is possible. The specification up to version six may only be available, but as these can still be read in Photoshop and GIMP I consider it still valid.

TIFF: May be powerful, but multi-layerd tiffs cannot be created by any modern open source programs. We could wait around for GIMP or others to enable this, but since that bug in GIMP was opened in 2006 I don't have high hopes of it being fixed soon. Plus, when other layer-based features become available in GIMP I doubt TIFF will be able to do the same

XCF: Already can be embedded or linked in Scribus, so is possible. Documentation may be sparse, but developers of the format are always at hand. The spec may be changing but when? Is it worth waiting, especially as GIMP has a history of slow development?

Open Raster: Since it's inception four years ago there's still only a few programs that support it http://en.wikipedia.org/wiki/OpenRaster In theory a good format to choose. If the GIMP plugin for the format matures and integrates then it'll be more of a contender

My vote goes xcf first, then psd, then open raster.

Can you see the benefits of a feature like this? In a sense it's like recreating the modular aspect of programming but in image editing. Need test cases? See Scribus or the Smart Object feature in some Adobe programs.