@Chuck,
Perhaps a little less far reaching than the fantasy land of a virtual world, maybe you could start with your chat bot being your personal trainer? You and the bot could work out the goals in exercising and diet. The bot might even run through the routine in its virtual world. You could have “reflection” time where you review your progress together. The bot could motivate you to stick to your regiment and reach your goals. Kind of an Eliza with a purpose… A virtual coach and training buddy, huh?