I'm not an experienced MEL artist, but isn't the proportional modifiction tool (prop mod tool) the basics of soft selecting. Could you not either, altar the basics of prop mod so you can apply a multiplier to the Modification Falloff value so you can change the rate of falloff like you see in 3DS Max.
Create a shader with a smooth circular Ramp for its color map. When the artist moves a models vertex, the entire model, or whatever vertices are selected would also move, but their distance of movement would be multiplied by the value ( based on the HSV scale, V=value of each color in the Ramp) closest to it. Lower Values would equal faster falloff, higher values would equal slower falloff. Artists could add as many colors as they wanted. This would allow you to customize the falloff speed and falloff distance.
When you turn soft-selection on, the shader would be applied as long as you have soft-selection turned on.
The problem would be that the model would have to either only be NURBS, or you would have to already have the UVs layed out, unless you projected the shader from the camera Z channel I belive.