What do you mean by the following sentence? Isn't better to actually use those namespaces for proper attribution and license information?
Yes, this is reasonable way to put attribution and licensing information in an XML file that is going to be interpreted by a machine, I was arguing that consistency and interoperability with HTML 5 (which uses microdata [1]) should be more important than keeping support for Semantic Web ideas that failed to get widespread adoption.
There are many complains, especially from web developers, about Inkscape generating verbose SVG files that are hard to understand and modify by humans. On the other hand there seems to be little demand for Semantic Web features.
[1] http://www.whatwg.org/specs/web-apps/current-work/multipage/microdata.html#l...