[allendoerfer]

This is the single biggest problem with Gimp.

As long as it is missing, you have to duplicate layers and do some mental version control, which becomes really memory intensive after you have descended the tree a few steps. That's why you cannot really recommend Gimp to anyone, who wants to work professionally with it.

It is also a reason why Gimp cannot get better at Photoshop compatibility, so the issue even blocks the second biggest reason hindering further Gimp adoption.