Protection of democracy as an urgent global problem
Without freedom of speech a project such 80,000 Hours would not be possible. Academics, researchers and other thinkers have limited influence in a democratic system; in an autocratic system they may have zero influence. For example, academics and researchers may decide that a certain policy towards AI is the safest policy, but they still need to convince legislators to implement that policy. In a democratic system that is already difficult, where legislators are more concerned with vote-winning near-sighted policies. But in an autocratic system academics and researchers may not be free to express their concerns, let alone influence government policy.
You list "democratic reform" as a promising area, as if democracy already exists in every country, and just needs some tweaks or improvements. Democracy is always under threat and is even more under threat at the present time for three reasons:
1) Artificial intelligence will make it easier for a small number of people to exercise absolute control over large groups of people. If an autocratic government has control of a preeminent AI, then preserving autocracy will be trivial.
2) Populist movements in many so-called democracies are in the ascendant (writing this in 2019). For example, in the USA and UK. Indeed, since 2008 the USA's Democracy Index score (by the Economist) has decreased from 8.22 to 7.96.
3) If China becomes the world's only superpower later this century then we can expect democracy to be under even greater strain, unless it adopts a democratic system in the meantime.
In short I think that you underweight the value of democracy and you underweight its fragility, and I think you should add "Protection of Democracy" as an urgent global problem and encourage intelligent and talented people to work in that field.
Campaign finance reform might be worth looking into, particularly the ideas of Lawrence Lessig. Mass media's influence could make this risky, though.