Add ability to embed or link xcf/psd files

Please note that linked bitmaps are already dynamically updated when modified from an external application.

I do realise that, but it would improve workflow if it could embed/link to xcf/psds. Look at Scribus as an example of why this is a good thing

xcf is an intentionally closed memory dump more than a format that a format that a library can support. So chances of supporting xcf as a supported linked bitmap format is quite low.

I requested this mostly because of how useful this feature is in scribus. It can even add linked svgs (as well as importing them). Would it not being added be due to svg spec?

Not to disdain your request. Tiffs (a well established format which support layers) can be linked inside an SVG.

Tiff's can be used to preserve layer information, but not layer blending modes, hence the request. Embedding or linking an xcf/psd would provide the most flexibility.

Could you elaborate? Tiffs created with Photoshop keep layer blending modes (how these are imported into inkscape, that's another story: transparency doesn't seem to be supported). What app are you using to create those tiffs?

I've used Cinepaint to create multi-layered tiffs that use layer blending modes. When opened back in Cinepaint or even GIMP each is able to see that the tiff has layers but none can preserve the layer blending modes for later modification. Of the two programs only Cinepaint can save multi-layered tiffs (see this bug https://bugzilla.gnome.org/show_bug.cgi?id=335975)

So, Cinepaint goes half way to solving this request in that it can have layered tiffs but it's missing the ability to preserve layer blending modes. In addition to that Cinepaint is currently not available in repositories on Ubuntu (I can't speak to Fedora or others) so it can't really be seen as a solution.

Perhaps, as you mentioned, tiffs saved in Photoshop can preserve layer blending modes (I can't test this) but it's a commercial, proprietary product that isn't officially supported on Linux or available freely, so cannot be relied on.

So, to reiterate my point, using psd and/or xcf files would make the best choice for this feature request.

The problem is that there is no good format for that. Sad but true:
PSD: propietary, the specs where disclosed up to version 6 or something, no longer open (unless you pay).
TIFF: extensible and very powerful, but there seems to not be a standard way of saving things in it (correct me if I'm wrong).
XCF: might do but the developers don't have documentation and it has limitations. Discouraged as an exchange format even by its developers. Will be obsoleted by GEGL and XCF2 will superseded it. That might do but it's too soon to know yet.
Open raster: what's exactly the status on this? I only see somewhat old news (about a year time).

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.