Yeah, there might be no end to how much you can understand about EA (or, more generally, stuff about the world that's relevant to altruism).

I certainly have my own blindspots but when talking to many other EAs I do notice that there a lot of topics they seem unfamiliar with:

• The extent of the uncertainty we have about the philosophy of mind
• Chances of being in a simulation/percentage of copies in a simulation and how that affects the expected value of various actions
• Philosophy of science/core assumptions behind how one thinks the world works
• Views of people in other parts of the world/society. 
• Relatedly, how futures led by influential people in other countries might compare to futures led by influential people in their own countries.
• Reasons to think that there are quite a lot of things that are low tractability
• Noticing how they came to be who they are/their place in history
• Impact of various activities on wild animal suffering

I don't claim to know everything about the above. And of course, others who know more about other things might notice that there are a lot topics I'm unfamiliar with. Some topics I haven't really thought about that much relative to a lot of people working at EA organizations:

• Anthropics
• Alien civilizations, how that affects priorities in longtermism
• Ethical theories that are super formalized (my moral anti-realism doesn't make me that motivated to look into them)
• Acausal interactions and decision theory

I don't think there's a single cause area where even knowing the sum of all human knowledge on the topic would mean you fully understand it