JPG supports regional focus too, in theory (Score 1)

There is still plenty room at the bottom, guys. Since the JPG format cuts up an image in 8x8 pixel blocks and compresses these individually, it should be possible to compress one block a bit more than the other. This can be used to implement regional focus, possibly resulting in significant space gains on many pictures while staying strictly JPG. I didn't experiment with this possibility (yet) so I don't know how it will turn out in real life.

Anyone care to make a nice GIMP plug-in for this?