I can't see a route from here to there. If such a thing were to come about, it would obviously have to happen via some form of (hopefully transitional) authoritarianism, since a century (give or take) of assiduous cultivation of a culture of greed has left our citizenries largely too enfeebled to willingly and/or competently participate in such a change.

Going from a couple of hundred very disparate nation States to a global benevolent & rational authoritarian regime isn't something I can imagine happening in the next 50 years or so without nukes getting involved. Admittedly predicting the future outside of immediate trends is a mug's game.