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.
The Akhal-Teke is a real horse breed that develops a metallic golden coat. A more fantastic version could have a coat the color of pure gold, or silver making the horse appear to be made of the precious metal.