The current draft of SVG 2 says that a conforming implementation must implement XML Namespaces. https://svgwg.org/svg2-draft/conform.html#ConformingSVGInterpreters
I guess it’s a matter of time when SVG 2 (or whatever comes after it) will make the XML serialisation optional in a similar fashion to (X)HTML 5. Google is already migrating Chrome’s SVG implementation from XML to HTML parser [1].
Inkscape should play nicely with the HTML 5 / Web Platform ecosystem if it wants to stay relevant in its field. It’s definitely too early to make any radical switch now since the specs are still in flux, though some legacy stuff like ref, cc and sodipodi namespaces could be dropped already in order to make SVG documents generated by Inkscape easier to work with in the most common use scenarios.