feMorphology radius - rectangle only

The current implementation of the feMorphology filter specifies a rectangle
(2*x and 2*y where x and y are the "radii") as the area from which the
max/min values for the current pixel. The effect of this is that shapes
within the input get "blockified" in the output (for lack of a better
word), particularly at radius values of more than a few pixels. This is in
contrast to GaussianBlur which preserves shape.

[Example comparing a simple circle - gaussianblur vs. dilate & erode:
http://jsfiddle.net/T3pb8/32/]

Would it make sense to add an elliptical or circular area option to
feMorphology that would better preserve shape between input & output?