I am not totally sure about national currencies but threat in job is absolutely possible to happen. Actually it is happening right now in the current scenario. I've known a lot of people who left their regular job coz they are already earning so much money here compare to how much they earned on their job.
I agree with you. Bitcoin can never replace local currency. These two currencies have different characteristics and uses so bitcoin will stay as digital money but using bitcoin can be a threat to jobs because people think it is much easier to use bitcoin than having to work literally.