What donkeys and mules absolutely need before they are usable:

• Gray dun for donkeys
• Genetics for black/brown and bay (decided that distinct black and brown are not critical for first release)
• Attributes that are not exactly the same as in horses - done
• Large standard and mammoth donkeys, big enough to ride, need to be more common so as not to disrupt game balance
• All textures need to have correct mule ears
• All textures need to have correct donkey tail
• Don't render height in the GUI for chested horses as there isn't room
• Write horse conversion to work with donkeys and mules
• Replace donkeys (and mules?) in village spawn structures, if any, with genetic ones
  There aren't any
• Make sure donkeys are configurable
• Prevent summon commands from making donkeys with horse-only genes or horses with donkey-only genes
• Optional bonus: Add a way to remove chests from donkeys and mules