I thought about such a feature myself and have created a Google Map of my own caches. I pinpointed the most NSEW cache co-ordinates and the "center point". However, drawing a rectangle is in my opinion not necessary and on many maps difficult to draw, especially, when you have been caching around the world. It will give curved lines instead of straight lines.
But having the NSEW/C co-ords visualized on a map could be a cool add-on feature.
Just an example how it could look like:
And with lines coming from the center: