I was thinking, instead of one income tax we break it up into income linked health tax, income linked education tax and whatever. Say each income linked tax could have a certain % of the effects of what currently is income tax, like each income linked tax could bring in 1/4 of the money and increase equality by 1/4 that income tax does. This way you could raise more precise amounts of money to spend on the particular things you want while not annoying people so much.
I just created a mod that does almost exactly this a few moments ago. But for some reason when I try to upload it to steam workshop the game just freezes and I get an error.
EDIT: Never mind, I read your comment wrong. I thought you were talking about simply taxing each income group differently.