I disagree that "France in the Year 2000" predictions were wrong. If judged by function rather than aesthetics they are more than half accurate.
First, there were industrial nations which were autocracies and lacked significant middle class. For example, Russian Empire of early 19 century. So the argument "no industry without middle class" is simply wrong.
Second, this chain of logic relies on every alien species having such social group as nobility. This is utterly absurd. For heritable social status, it is necessary that upper classes have the same (or lower) number of (surviving) children as commoners, otherwise in a few generations everybody would be a nobleman. This only happened because humans are poorly adapted to civilized life. For civilizations that exist for millions of years, evolution would definitely fix this.
We technologically plateau because we reach technological limits. There aren't many important technologies not invented yet, things like nanorobots, compact fusion reactors or Dyson spheres are impossible. Whether AI is developed or not is irrelevant. After a century or two of stagnation, civilization runs out of resources and declines to pre-industrial level. This is our future.
For this outcome, everything below has to be true:
Given that, 95% claim is very overconfident.