> If your goal is to move the us to post scarcity world you have to come up with unlimited free and (relatively) clean power source.
Not a problem. Nuclear fusion. And before someone goes off on a tangent about, "It's only 10 years away for the past 60 years", that's because The Powers That Be won't give it - and by extension, pure science - the funding it needs to happen. The Defense Department budget increases by $80,000,000,000 for the 2021 Federal Budget. No one batted an eye. I guarantee you, if you throw $80 billion at fusion for 60 years, humanity will solve it. The pathetic $5 billion here and $2 billion there won't cut it. You have to sink real money into it.
> After that someone needs to figure out how to turn that unlimited energy into mass.
Funding. Once fusion is solved, throw $80 billion at this problem every year. See above.
> Then someone needs to figure out how to 3D print things atom-by-atom using the previous technology.
Funding. See above.
> After that money loses all meaning and there is no longer income inequality.
After that, we become a reputation-based economy, like Star Trek. It's about what you've done, not how much you have.
None of this will happen until we stop allowing single individuals to hoard enormous amounts of wealth that could never possibly be spent in their lifetimes.