I feel a weird disconnect on reading comments like this. I thought s-risks were a part of conventional wisdom on here all along. (We even had an infamous scandal that concerned one class of such risks!) Scott didn't "see it before the rest of us" -- he was drawing on an existing, and by now classical, memeplex.
It's like when some people spoke as if nobody had ever thought of AI risk until Bostrom wrote Superintelligence -- even though that book just summarized what people (not least of whom Bostrom himself) had already been saying for years.
Huh, I feel very differently. For AI risk specifically, I thought the conventional wisdom was always "if AI goes wrong, the most likely outcome is that we'll all just die, and the next most likely outcome is that we get a future which somehow goes against our values even if it makes us very happy." And besides AI risk, other x-risks haven't really been discussed at all on LW. I don't recall seeing any argument for s-risks being a particularly plausible category of risks, let alone one of the most important ones.
It's true that there was That One S...