The opportunity would be reduced for tax avoidance, both technically (as you can't shift income from one form to another with a lower rate) and morally (as everyone is having the same proportion of their pre tax income removed), so I would expect it to reduce slightly.
However, I don't buy into the idea that inequality is something the state should actively work to reduce. The most cited piece on it (the spirit level) is flawed due to cherry picking, and the claimed correlations disappear when you pick different years to the one quoted, and stop cherry picking the countries to analyse.
To me, the key part that matters is ensuring everyone has their basic needs met, not to compare their income to others.