What was Karl Marx's original plan for communism?
Marx did not have a plan for communism. Marx had a scientific theory predicting that communism will replace capitalism as human progress. So there is no such thing as a plan for communism. Just as Newton has an idea of gravity, Newton never planned a solar system. Marxism is a theory explaining the outcome of human progress after capitalism.
First, human history tells us human civilization has changed over hundreds of thousands of years. Everyone can observe that the world is changing. Anyone proclaiming that capitalism is the last stage of human civilization and that human civilization will stop evolving further is not learning the history. It is for sure that human civilization is evolving and capitalism will finish sooner or later. This is a historical trend nobody can prevent from happening.
Second, capitalism is evil. At beginning of the capitalism, Britain employed child labor and made workers in Britain miserable. Later the western powers colonized the world, waged many imperialist wars, traded slaves and opium, and made colossal humanitarian disasters. Even today, the US-dominated areas have wars, terrorists, and refugees. The US-dominated world is a capitalist world full of wars and famines. Capitalism puts corporates' profit above humanity. Anyone who has a human conscience should support communism and against capitalism, especially against the military-industrial complex that Eisenhower warmed us. If human civilization is evolving, we should strive to end capitalism.
Marx had his conclusion that communist society will come after capitalist society after he studied capitalist society thoroughly. His famous work is The Capital. It is an economics theory. The theory is still valid for today's world economy. If one wants to understand why and how the world is, he or she should study The Capital by Marx. Communism is not a plan by Marx. It is what the world will evolve into based on the economic theory developed by Marx.
Because communism is not a plan, there is no cush thing as it fails. We can only say that communism is not realized yet. If a human is good and is willing to end evil capitalism, it will evolve into communism eventually. Russia tried and failed. But it is a good try morally. China is doing a good thing for the world by promoting mutual respect and win-win cooperation in international relationships. We don't need to label it as communist or capitalist. All we care about is that the advocation of mutual respect and win-win cooperation is morally good, and we should support it. Xi has a vision of a Shared Future for Mankind. This is a good vision. We don't need to label it as capitalist or communist. If we keep our human conscience, we should support Xi's vision of a Shared Future for Mankind just for the sake of humanity.