Speaking as someone who has written many well-received essays on LessWrong, I feel like you're approaching the problem from the wrong angle. IMO writing a good essay shouldn't be a goal, it has to be a side effect of doing interesting intellectual work.

For example, there's someone on LW who wrote a chatbot that successfully hypnotizes people over IRC. Would you read an essay about that? You bet you would! There's also someone who sold drugs for bitcoin, and someone who doxxed drug lords, and someone who won AI-box experiments, and someone who independently invented cryptocurrency... My own most successful essays on LW came as as a side effect of my work on decision theory math, which had other nice effects as well (like being invited to speak at conferences). Even Eliezer's essays were a side effect of his attempts to figure out friendly AI, rather than "hmm I want to write something interesting today".

So, instead of mulling over which obvious thing you'd like to write about, try to do some novel work that interests you on its own terms! When you try to describe it afterward, I promise you the words will come much easier.