Plagues and other great diseases are important parts of history and some settings. They defy man and may even defy God in their swift and terrible punishment upon the body of society.
My issue with modifying/removing dwarves and elves is that the PC’s may want to play them.
One of the most powerful tools found in the World Building 102b article is the Worksheet. Here is a place to put the settings you might make with them.
A world whose lands are made up of huge terrain spheres that rotate constantly with most portion underwater. As time passes, the shape of the bodies of water change, landmarks shift inside the new border lines, and mountains tilt to different degrees. Land dwellers are gypsies that can never build anything permanent, and somewhat ironically, the only stable settlements are large structures built at sea.