Earlier quoted context omitted.
This tripartite split (elite, bourgeois, poor) is a very old one. I am sure I read a paper in an undergrad poly-sci course that analyzed the fate of nations based on which two teamed up against the third. Elites+poor is a pretty dangerous combination because they end up catching civil society in the pincers.
The author did make the argument that revolutions that start from the middle are usually less violent and chaotic. I don't have the relevant education to know if that is true but I do know that I'd rather lead a revolution than be the victim of it. To be fair to the author, that is his ultimate point. It feels to me that the idea of sacrifice has become a secular heresy. Humility as well. If the middle class has any…
I'd honestly ask a slightly different question : how much longer will the lower and middle classes pose a realistic threat to the elites?
To date, economic and social elites have always been at the theoretical mercy of the masses simply by virtue of vastly inferior numbers. We're not that far off from a day when - as a result of technological advances of various kinds - a small minority could feasibly defend themselves both physically and politically against the rest of society.
To me, that's honestly the real ticking time bomb. People can change, grow and adapt to any number of situations - and are remarkably good at finding common ground with their neighbors when necessity dictates. However, once the masses lose their ability to meaningfully threaten the elites, the entire question becomes moot and the ship will have sailed for a long, long time.