As an enormous fan of Crash Course, I would be loathe to see it end any time soon. As such, I want to offer yet another option for a future CC endeavour: philosophy.
I think this would be a great subject to tackle since, like history, philosophy has a kind of timeline that can be used as basis for planning out the various episodes. So, for western philosophy for instance, it could start with Thales and progress through Plato, Aristotle, Augustine, neo-Platonism, Thomas Aquinas, scholasticism, scepticism, empiricism, humanism, existentialism, postcolonial theory, etc. The same could be done for eastern philosophy as well, with plenty of overlap I am sure, although I am far less familiar with the exactitudes of that subject.
Moreover, I think philosophy would be a good subject for Crash Course because it isn't just about facts and dates; rather, it will provide viewers with a wider understanding of how certain ways of thinking developed and the ability to think more critically about their own surroundings.