Let's suppose for a moment that we accept the thesis that due to automation, there won't be much work for humans in the future. Instead of taking wealth from the smaller number of humans who are creating that wealth and giving it to those who are not, why don't we just accept that we don't need so many of us any more? Let the extras die off naturally (note to angry skimmers: I SAID NATURALLY) and migrate to a new low…
Enough people want to leave a biological legacy, so halving population each generation seems optimistic. (yes, many people don't want children at all, but many that do also want their child to benefit from having a sibling. I will assume these numbers cancel out.)
So it will take centuries to get down to the "low millions" range, even longer if lifespan extension pans out.
Automation, meanwhile, is already happening, and the current wave is more likely to be felt in a span of decades rather than centuries. Unless you count "starving in the streets" as a "natural die off", redistribution is going to be needed regardless.