High bit depth support and non-destructive editing will be delivered through GIMP's integration of GEGL, the Generic Graphics Library, which is a graph-based image processing framework. "GEGL provides infrastructure to do demand based cached non destructive image editing on larger than RAM buffers," GEGL's website explains, "Through babl it provides support for a wide range of color models and pixel storage formats for input and output." GEGL also plays a role in enabling GIMP to have a high-quality colour management workflow, but this last feature will also require a lot of work on the GIMP core.
Nordholts explains that the GIMP already has a core fully capable of offering high bit-depth and non-destructive editing, but that "What needs to be done is adapt code so that users can make full use of this currently isolated core." He added: "It is impossible and pointless to speculate about a specific date when this will be complete. We can only establish that work is being made and will eventually be finished."
As for the bit-depth issue, Nordholts assures that the legacy code in the GIMP that assumes 8 bits per channel doesn't need to be rewritten- it needs to be replaced by GEGL. Some wrappers might need to be written in order to provide support for legacy components within the new framework, "but that's not really rewriting code". "I don't really see any major challenges regarding higher bit depth, code just needs to be written."
Another common complaint regarding the GIMP is its rather diffused and unintuitive interface, with its multiple windows. Nordholts says work is also being done in this area. "There have been discussions about a single-window tabb-based interface that can probably interest a few people."