There won't be the big UBI day, where we make the big switch globally. It's a creeping expansion of social benefits and transfer payments and an easing of work conditions. Some people will somehow stay in the unpleasant jobs, by inertia or the unfairness of a class system or, increasingly, by wages that compensate for the trouble. People will drop out of individual job categories and certain businesses become unsustainable; society will adapt around it, with automation or higher prices.
The conclusion for the individual is to not tough it out in a shitty job, instead look for opportunities where companies will pay a contractor or company to do work that used to be done conventionally in-house for a wage. Also, and I hesitate going that route, don't see the redistribution opportunities as shameful handouts, but rather as an income stream that will make up a larger and larger pie of the economy.