This is a very interesting question. Obviously 「働きたい」and 「働いてほしい」are different. So I guess the question is about the difference between (1) 「医者になったら　地元の病院で働いてほしい」 and (2)「医者になったのなら　地元の病院で働いてほしい」 I might say (1) to someone who has decided to go to a medical school. Then the meaning would be something like, "One day when you are qualified as a doctor, it would be great if you could work at a hospital in your hometown". I might say (2) to someone who has just become a doctor. Perhaps this person has studied medicine at university and he could have chosen different careers, for example, as academic researcher, Ministry of Health official, etc. Then the meaning would be something like "Since you have chosen to become a doctor (rather than other career options), it would be great if you could work...etc.". The difference is subtle and the nuance depends on the context, especially in the case of (2).

医者になったら　 　　--> 你成为医师的时候 （他现在还没成为医师） 医者になったのなら　 　　--> 既然你现在是个医师， （他现在已经成为了医师） 明白差异的原因需要详细语法的解释。