Wishlist Item : Tracing SVG Filter Effects

It would be nice if it was possible to trace an SVG Filter Effects area (i.e. transforming them to vector shapes) without passing by Convert to Bitmap (without beeing a programmer I expect that could be a very interesting and promissing programming experiment). This area could be determinated by a vector shape drawn on top of the filtered object.
In the past, Freehand had the possibility to trace any rectangular area containing vector or bitmaps and that was already very useful. But with all the nice transformation tools included in Inkscape that could become a must !