I've done some digging, and I saw external CSS support was already planned for two consecutives 'google summer of code', though it is still not possible using them in inkscape, be it classes or even getting them to display properly.
I've attached three files, one being the original file with the style attributes inline, it shows quite well in inkscape, the other two being a css file and a svg file with references to this css file. When I open the latter, only a black shield is displayed, as no style information is loaded.
Additionally to getting inkscape to at least display the SVG correctly, I'm still pondering on how to implement the creation of the file in inkscape, there should be some possibility to apply a certain style (defined in a css file) to a path, so I wouldn't have to change the SVG file later to apply all styles.
At the moment, it would suffice to get Inkscape to display the files correctly, as I still do some tidy-up with the resulting SVG files, so I can also replace the style commands with the correct class definitions...
