MAX's own blur effect allows to specify the area to be blurred via material- and object-IDs, but by this the blur of course extends beyond the edges of the respective object, plus the object itself (for example a plane mapped with some fabric-texture) gets blurred too.
The frst problem mentioned appears to be fixable, since I've seen a render-effect plugin (can't remember where) that allows to blur the image based on an object ID, and makes the blur being masked to "stay inside" the area to be affected. But even this plugin has the problem of the original object getting blurred too, so this wouldn't work for textured objects.
I guess it would be required for the image to be rendered in 2 layers internally, and then composing the object causing the blur (in this case the fabric) on top of the partially blurred background.
It would be even better to have a plugin, that allows to apply all available render effects, based on their position in the scene, relative to other objects (or pixels). So that you can, for example, not only blur the image behind the fabric, but change its colors and contrast as well. So instead of just limiting a render-effect to material-IDs, object IDs, Z-position, you could also limit an effect to something like "behind object x" or stuff like that.
Would this be possible?