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 guess those people who quit their job just for this is a coward, digital world is unstable wherein everything changes in just a matter of seconds. Even it helps to earn more money, bitcoin is not a threat to jobs but on national currency, why ? because somehow at some point bitcoin takes the place of a national currency as a medium of transaction which is supposed to be centralized.