Let's say you had an instance variable called state that can represent three states: HIDING, CHASING, or ATTACKING. Without Enums, the best approach is to use a Number for this variable, and then declare global constants in the following manner: HIDING = 0, CHASING = 1, ATTACKING = 2. Now you can use these constants in your code with full control over them in case things were to change.
That works fine for one object, but now consider you have 15 different objects with different state values. That's a lot of global constants and can make things very unclear in the code. This issue could be eliminated if we had an Enum instance variable type. With an Enum, every state would be self-contained and it could be easily referenced in the code.
Is this planned for a future release? If not, why not? Instance Enums would be handy ex. intelligent enemies (hiding, chasing...), characteristics (sharp, smooth), etc.