MC should be able to recognize different type of images, and show them accordingly imo. Just as folder.jpg is used today, you could have artist.jpg (artist image), front/folder.jpg (front of CD/DVD/BR covers), back.jpg (back of CD/DVD/BR covers), series.jpg (series image), season.jpg (season image) and so on. The correct image should be shown in the correct views. Either automatically, or perhaps even better; Check boxes in the theater view options for each view. This way, artist images could be shown when viewing artists, series images while viewing series, front/folder while viewing albums and back covers should be shown when hovering the mouse above the cover, or when you select and hit enter on a cover in theater view as an example.
To limit this to Covers and Artist only, and leave us with no manual control over it is not great. Some might like this to be automatic (like it is with artist images today), but may of the MC users I know, use this app because of the way you CAN control things. Cover/illustration images is not MC's strongest side.