The Synology expansion units have a completely different device connectivity structure that would be very difficult to emulate, while we generally are just adding SATA ports on top of those that are natively embedded in the platform. Bluntly, our way is simpler.
If you really wanted to make the graphic, somehow grafting the images and logic in from one of the other units would probably be the easiest way. But it would get overwritten on each upgrade, and it is, again, purely cosmetic. For most of us, not really worth the cycles.