OK, so I was thinking, almost every world has a theme right?
Wizard City- Magic Krokotopia-Egypt Marleybone-London MooShu-Ancient Japan Dragonspyre-(almost every video game that has worlds ends with the lava place) Grizzlehiem-Vikings
Here are some theme ideas i came up with:
Paris African Plains Antartica/Alaska Amazon Wild West Island (Hawaii or Jamaca) Native American/Indian Outer Space New York City Austrailia Outback The Sky/Clouds Midevil
Dragonspyre is based off the Byzantine empire, I believe, and some of the worlds you mentioned go together sort of. Also, someof the ones you said would fit too well together would existing ones. But as long as we're posting ideas, a Jungle-ish themed world would be nice.