Krita has CMYK, and very good non-destructive editing these days. It's my preferred photo editor, including for the occasional magazine ad work I do. It also has great support for PS files, including smart layers, etc, plus it has layer effects, masking, filter layers, GPU accelerated canvas, and G'MIC support covers a lot of the fancier pbotoshop stuff like content-aware fill. IMO, for the workflow and interface alone, it's leagues ahead of G***.