Steve,
Tracing any design would still export a SVG file with RGB colours when you save it. For the moment once the SVG is imported in Scribus, I have to reencode colours manually, remove unused colours then save as an EPS with a specially sized document and store the little fellow in a safe vault... not exactly a model of convenience. Fortunately good logos only have a handful of colours and sensible design means you create a PMS / Process colour text file as a memory aid (usually on customer requirements anyway) and supply that to your customer in the logo package.
Therefore my second question : is it on the roadmap to create a specific Inkscape SVG which would support features that SVG standards do not support (even if it has to be a mode, and therefore get away from pure SVG and not be backward compatible)
Cedric
perhaps you could produce your logo in an application which does support CMYK... then... in Inkscape 0.45, trace this. I used a higher number of color passes.
Its not 100% inkscape, but maybe just right for logos ?
Also, I believe SVG does not support CMYK colour space colours (as per Tavmjong Bah's brilliant userguide), and this is important for logos and even EPS export gets imported in Scribus with RGB colours....