Sunbeam: I've already started working on this, called "additional artwork classes" (currently WIP). It will allow you to freely define whatever image-types (or classes) you'd want to add... however, the current way of finding images will not change basically, that is, no XMLs will be required but images in respective folders or ZIPs, containing PNGs named after the game/machine or software.

A mind is like a parachute. It doesn't work unless it's open. [Frank Zappa]