Hi there I am new and all, but it's a bit weird that CMYK still not supported till today.

is it not possible to even just use Scribus' engine or just use the core that handles CMYK or something?

like the functionality already exists in other opensource application, why not even copy it and credit the authors for it?

The problem with Cairo is that it doesn't yet support CMYK, or, to put in in a more technical language, it doesn't yet support color management, color separation and spot colors. This is not because Cairo folks are not interested in that, but because they don't have a dedicated developer to work on it, and it's a lot of work.

http://libregraphicsworld.org/blog/entry/getting-cmyk-colors-from-inkscape-to-scribus