My idea for a world: Wonderland (yes, like Alice in Wonderland)
This world could be a world just for fun around level 20. I imagine this would be a fun world and considering the creativity I have seen from the past worlds, you could pull of an interesting world.
Copyright would not be a problem seeing that it ended in 1907, and through the looking glass until 1948. Disneys cartoon and movie still remain in copyright. This world could really push the limits of crazy and nonsensical. I'm talking an opportunity for mobs to be upside down, or the battle to take place backwards (the last person who usually goes goes first). Bridges could move and pathways could be dominoes. Quest to help tea cups and the final battle of course be the red queen (or alice if you want to throw us for a spin). Smaller bosses along the way could be The Mad Hatter (that could be a dungeon considering he is a main character in the original book).
The world that is everything it is not makes for the possibilities for theme style clothing, hair styles, mounts, house themes, new spells, pets, and whatever else you can think of. Overall it would be a fun world to explore and quest in, and I hope you consider it!