Can't see that happening. Every country would then have to be pretty well exactly alike....same health systems.....same pay for jobs....same cost for housing....etc etc. Total freedom of movement would cause absolute chaos. Everybody would need to be the same as well.....same motivation....same skills....same chance in school.....kind of sounds like a SciFi movie. Will it happen some day a zillion years from now?.....who knows.
We have a lot of work yet to do, it's true.
But literacy rates are much better now all around the world....vaccines and such have helped boost global health. Women's issues...so important for economic and social progress are being loudly trumpeted, and more-and-more acted upon. We can communicate a lot better now.
Look, there's this idea that everyone wants to move somewhere else....I think a lot of people are happy as can be right where they are....most people perhaps. Family connections are important for instance. So I think if you did drop borders right at this moment....most would probably stay right where they are....heck it's where they have a job.
So who is moving about? Or who would? Displaced people. People under threat of violence. People with no hope of bettering themselves financially. These things can be addressed.
But you know, you can look at the EU, say Polish immigrants....it is true that many moved to the UK seeking better conditions. But the flow has slowed to a trickle. Many have moved back. Some sort of equilibrium has been reached.