There is a good case for allowing a child element that defines character information (a la glyphs) for its parent (or sibling) shape, making it an ad-hoc glyph.  It would be rendered in all user agents, and for those that support this functionality, it would also impart textual information.  The shape would be selectable just as text.  It would be easier to author than the equivalent SVG Font, and though it wouldn't have all the functionality, it would still be useful even in UAs that do both.  Think of it as alt-text for a shape.