A key issue in thinking of future left is the failure of much marxist theory: historical materialism and productive force determinism are fallacious theories and every time leftists cite them they invoke all the controversies that exposed them, left and right.
Marx’s views of world history are very dated, and his theories of economic history in particular miss the point that culture is a far broader category: the marxists end up the worst offenders of economic reducitonism. The old debates over idealism, materialism and historical materialism are burdens of the left: they may as well be left behind. The same is true for much of the dogmatic marxist canon which routinely turns off those who encounter socialism/communism and must deal with the de facto monopoly they wield on the ideas for social transformation.
Source: ISO refounding an opportunity for a new left??? – 1848+: The End(s) of History