Specifically, interested in examples of technologies where a) people who actively worked on it genuinely believed that if they can do it once, it'd (eventually) be very cheap and scalable, b) we eventually did develop the technology, c) it ended up not being a big deal anyway because it wasn't very scalable and d) in hindsight, we still believe that had the technology been cheap and scalable, it would have been a pretty big deal.
Also would love to see statistics on how frequently this has happened in history, though might be pretty hard to draw a reference class well.
I think a lot of EAs have the implicit assumption that if something can be done once, you can probably (eventually) do it cheaply and at scale. For very EA relevant technologies, I think many people think this applies to human-level AI, anti-aging treatments, and cultured meat.
I'm curious how frequently counterexamples happen. The only counterexample I'm aware of is alchemy. Transmuting base metals into gold was something multiple civilizations literally wanted to do for millennia, we eventually figured out how to do it last century, but the discovery turned out to be at best an academic curiosity since the energy requirements were too massive.
I'm interested in this question because having base rates on the scalability question would be really useful to form some very weak priors on P(technology radically changes civilization | radical-seeming technology was invented). For example, if, after an extensive search, alchemy was the only interesting example, we can conclude that our initial implicit assumption that "once you can do something, it can be scaled (EDIT: though political/cultural resistance can still mean it won't be scaled)" seems like a very safe one.