I wonder if we will be ever rid of a “third world”, the Pareto principle, also known as the 80/20 rule, states that there will always be a minority of things. Of course, as things get better over time, definitions will change.
The 20% can be broken down even further too, 20% of the top 20% and so on… This works in nature too, 80% of the planets rotate around 20% of the stars, 80% of software glitches are caused by 20% of bugs, 80% of sleep quality occurs in 20% of sleep…
So, maybe we will never be rid of the Third World, there is likely always going to be someone better off than someone else, I'm optimistic things won't be as bad as some worry about.