So for the theme I was thinking of having custom art that reflects the main focus of the cabinet: Multiplayer- particularly 4-player. My initial thought was a big side-art melee showing TMNT vs X-Men vs Simpsons (and maybe some Battletoads, NBA (Jam) players, Gauntlet, and D&D warriors thrown in for good measure.)
Ooh, it just occurred to me that I could have the CP art actually show three characters in each player's position, reflecting the characters from those three machines. So the first player position could have Michelangelo, Wolverine, and Homer!