Joseph Schumpeter thought that the capitalist system would end someday. I'm not trying to make an argument for why, I just remember a sidebar in an econ lecture about on his ideas where this was mentioned. He was a capitalist heavy weight, creative destruction and a bunch of work on the business cycle, very pro entrepreneur.
Or modified-capitalism just continues to be the best economic system, and post-capitalism never becomes a thing. I figured we wouldn't be making the mistake of assuming capitalism is going to come to a crashing halt after the whole communism thing. Capitalism today is not capitalism that existed 50 years ago. "humanities social system" in the form of the way nations organize and move resources around is in a constant state of flux. Generally, we call it capitalism, but to assume it is one system over the last 200 years is not very true at all.