I could foresee lots of people quitting to learn skills for more rewarding jobs. You might see that jobs like a janitor, garbage man, and service reps at abusive companies start commanding higher wages since people don't want to do them.
Now workers have the leverage to decide not to work doing something they hate unless they are paid enough for it.
Creating free education programs for careers in demand would really strengthen this effect and I think would improve society as a whole. People will be rewarded for doing menial or dirty jobs rather than looked down on by society.
Jobs that are currently mostly done by people with no other choice, and hence can pay as little as they want, will have to pay better or be part time or some other benefit if they really need to get done.
And then, if a crappy or mindless job ends up paying $30/hour, people might do it because they want the extra money, not because they need it to survive.
UBI could serve to further entrench an existing exploitative pattern, which currently exists because some things are "paid" work and other things are not.
Fascinating.