Better handling of SVG's <defs>

In Inkcape 0.48.5 r10040 (on x86_64 openSUSE 13.2) I found this: You can define some object, and convert it to a marker. The the object disappers, and it seems you can never update that object. When saving those objects are put into DVG's <defs>.
When browsing the SVG specs, aI have the feeling that <defs> is like a special layer that is never displayed, with the only purpose to contain elements referenced by <use> in other layers.
So I wondered why Inkcape cannot provide some means to edits the "defs layer". My initial thought was that Inkcape could create a spacial layer tha you can edit like a usual layer, but the I realized that such symbol-like objects may lie on top of each other (e.g. each being positioned at (0, 0)). So maybe a stack of layers is actually needed, or maybe a special layer attribute "defs" indicating that these layers are never displayed, but the objects are put into the <defs> section of an SVG file.
Maybe an easier UI for symbol libraries can be defined along with this.