Here's a chart that tries to show the decline of upward mobility in the U.S. with an article that explains it. While, from the reading I did while trying to find this - which was not a huge amount - it does appear down, somewhat, worldwide, it is in a much sharper decline in the U.S. on average. This, of course, is in comparison to European nations. Not a true "worldwide" comparison.
The world just went through massive war that destroyed nearly all of Europes infrastructure and the demand to fix it mostly manifested as opportunity for Americans. Since then Europe has rebuilt and both India and China have arrived on the scene as powerhouses of their own. We will never have the same opportunities that we had then again, or at least we should all pray we don't.
Also I like the stagnant wage growth numbers because it demonstrates that the corporations are no longer the gatekeepers to economic opportunity. If you're more likely to make money starting a business than getting a job somewhere and working there 30 years, this is good for everyone because their economic prospects aren't dictated by McDonalds and General Motors. It means a more diversified economy, more opportunity beyond the beaten path, and more creativity driving economic growth.
I'd also like to see the criteria for "upper", " middle" and "lower" used in the chart about income distribution. Judging by the first graph of "is it all bad news?" I'd say it's a hard dollar amount delimitation, a very bad metric, because while that would appear to show a bad trend, all it shows is that more people have higher amounts of money. The only way to get a clear picture is to weight income/wealth with purchasing power as the delimiter between classes.
Another note on this first graph, it clearly shows that less people are in the lower class and lower middle class, and more people are in the middle, upper middle and wealthy class with each graph since 1967, which means people have gotten richer and as a whole life is getting better for people economically. Ideally what you'd want to see is the bars to the right of each sample get bigger and the bars to the left get smaller with each sample, and you almost see exactly that. I'd like to see the same graphs in 20 years and that will tell if upward mobility has actually decreased. I'd also like to see this graph weighted with purchasing power.
From those graphs, upward mobility looks perfectly fine, I'm getting the sense it peaked about 20-30 years ago, but has not had a sharp decline and is definitely still higher than it was 50 years ago.