animateMotion along things other than paths?

Just for fun, I tried using

 

<animateMotion dur="5s" rotate="auto" repeatCount="indefinite" >

    <mpath xlink:href="#E"/>

</animateMotion>

 

where #E actually refers to an ellipse rather than a path.  (Yes I am aware
than I can make an ellipse using <path>)

 

Of course the spec [1] requires that the referenced geometry must be a path,
but it made me wonder if this should not be extended to simple things like
<circle>, <ellipse>, <polygon>, <star>, <rect> or even <use>. (Use would
actually be quite handy for the thing I am working on at present)

 

Cheers

David

 

[1] http://www.w3.org/TR/SVG11/animate.html#AnimateMotionElement