Actually in North America we could have had a working post-scarcity since the 1930s.
How does that work? There almost wasn't enough food to go around in the great depression, and plastic was an advanced new material hard to come by from the 40's through the 60's. Electronics took a long time to be produced in any significant quantity too. And what about land?
Not sure where you are getting the philosopher king thing from?
Plato said everything would be great if we had the smartest people in charge. He called it the philosopher king, others call it technocracy. In ancient Greece I probably would have thought it makes good sense.
In practice, thousands of years on, I think history has shown that there were always smart people and good ideas around; the shortage was of incentive for those with power to implement them, instead of just entrenching and enriching themselves.