In a hundred and twenty or thirty years or something, the dollar will have inflated by 1000 times, so a billion dollars then will be equal to a million dollars now. It'll cost a billion dollars for a nice four bedroom house.
But we'll have had a hundred more years to produce anti billionaire propaganda, so a lot of people, especially teenagers, will need it explained to them that being a billionaire isn't so bad now. The Marxist-Leninists will all be saying that Cyborg Bernie Sanders is an evil billionaire, and us reasonable leftists will be explaining that a billion dollars is just what it costs these days to own a residence in your home state and also in DC, which is necessary for working as a senator.
What we'll really need to look out for by then is the trillionaires. Good for nothing parasites. There's no excuse for one person to own a trillion dollars while there are people living on the streets who can't even afford a measly ten thousand dollars for a cheeseburger meal.
At this point I would be surprised if it makes it for another 30 years.