Guaranteed Minimum Income and Basic Income are 2 different things (this article discusses GMI).
GMI means that you will get enough money to bring your income up to X (in this case $20k.)
BI means that every citizen gets Y dollars per year unconditionally.
GMI is only a net benefit if you make less than X. BI is more complicated because you have to decide at what income level should the BI be income neutral, i.e., how much do you have to make before the BI you're receiving and the extra income taxes you're paying are equal.
> I haven't seen any analysis that would answer the question who exactly would get richer / poorer and how much.
The reason you haven't heard this is because it's completely up to the implementation details.
If for example the government decided that for people making $50k a year the BI should be income neutral, then it would be a net benefit for all people under $50k and a net detriment for everyone over that.
>What about teachers, software developers, bus drivers, lawyers, etc?
In this hypothetical scenario some teachers, software developers, bus drivers, and lawyers would benefit, and some wouldn't.
>It removes disincentives to work. I'm not convinced about this, you could argue the opposite is true actually.
This is only true for BI, not GMI. GMI adds a huge disincentive to work for less than (or close to) whatever the guaranteed minimum is set at.