You cannot implement communism because it is the Utopian end point of a social progression curve that includes capitalism, and will ultimately end up in some form of competition-inflected social democracy. Enforced communism fails; it is based on a lack of democracy, choice, equalism and forced redistribution. It never has or will work. Ultimately the inequality of capitalism will form the equality of a Marxist social democracy - where the number of people relying on welfare grows and grows until the welfare state is larger than the productivity of the state, and so becomes the state, with the state providing for (nearly) all. That that was Schumpeter's arghument, anyhow. It's the one I'm inclined to agree with, although like him, I question the pace at which it will happen and the reality of human nature allowing it to happen.
Marx and Engels based a lot of their work and assumptions on deeply floored evidence, interpretation and understanding of the technological innovation that would occur - based in no small part of completely misunderstanding the part competition has to play in capitalism as a driver of productivity and wealth for all involved. The working class of 2014 are far better off than the working class of 1814, and the working class of 2114 will be better off than today's. They will almost certainly be worse off in relation to the upper class of 2114, but their base level of comfort will still have gone up. This is where Marxists and leftists in general confuse inequality for increasing poverty, or any sort of unfairness at all. The capitalist establishment requires the lowest common denominator to be wealthy enough to buy from the rich producers. Consumption is the core of western capitalism, and is the main focus of long-term reforms in China. Capitalism requires it's population to be wealthy and happy. Yes, the rich get richer faster, but the poor get richer too - infrastructure, food quality, amenities, housing - all steadily improve as time goes on. It is not direct trickle down in raw financial terms (that does not exist) but the rich investors elevate the poor consumers to a maintain their own growth. In communism, the inevitable top strata have absolutely no inclination to do that for everyone else. Communism in theory is Utopia, but in practice, utter hell.