I thought of some things a stereo picture, which one can now make even automatically with a mobile phone, could help the GIMP do better and mention them here in case someone would like to program them.
* Create defocus: a picture can be taken sharp all over, and later blurred as much and however you like gradually away from items at chosen depths, with sharp objects in front blotting out blur behind as with a real lens.
* Select objects for editing: a person, for example, will have many different colors, tones, and textures, but stand at a distinct, only gradually varied depth.
* Stitch photos: knowing objects' depth could allow adjacent photos' projections to be adjusted perfectly to new overall projections.
There are more details, a few more ideas, and tips on taking 3D pictures here: