For some interpretations of this dengerous oxygen deprivation, you can stop now. Support has been added to both babl and GEGL to handle CMYK images - which can be be used and tested on the commandline - and used in the experimental alternative GUIs for GEGL that are in git. If someone hooks this code up to GIMP I will be diverting some more of my already thinly stretched attention back to the CMYK code in babl and GEGL to make it fast as well. :)