This idea has the Empire MineCast stamp of approval. I'll elaborate on my idea of it: A wasteland underneath, but 4 guardian statues (think Atlas from mythology) holding up a glistening steampunk city, complete with airship, etc.
I think a giant tornado in one corner, with houses it is about to hit on the other residences would be terribly cool.
Make a creeper/ghast/blaze temple to honor all of the explosive mobs. The 4th could be a GIANT diamond/obsidian piller.
You could make the 4 different residences different wilderness biomes such as desert, tundra etc. Also high in the sky above the biomes you could make floating islands or something like a cloud kingdom/city.
make an amusement park, Make some Epic Wool Statues A pirate bay with loads of Epic Pirate Ships the London 2012 Olympic Games spoof. (Minecraft Games) include really cool events
Save the bottom for something else and combine all 4 res into one big on above 135 blocks. You can make a sky districtwith airships and stuff.
I'm pretty sure you can't change the rules after this is posted. You changed the number of entries from 20 to 50.