I mean, it's worth asking, but anyone with a good niche would be smart to not post it publicly unless the benefits of publicity outweigh the risk of competition.
Sure. But most good passive income ideas are good because of how easy they are, and because they're the perfect size for a small market. Usually even one more competitor entering the market is enough to significantly disrupt them. If you are sitting on one of those, why would you post about it in an HN thread that will be archived and trawled by capable competitors specifically looking for ideas? If it only takes one competitor to disrupt your golden goose, why would you post about it here?
While there are many interesting ideas in this thread, I expect there are a fair amount of people lurking with much more profitable and higher leverage products. So maybe just take the thread with a grain of salt and don't think of it representative of a ceiling on what's possible to build in 2019.
I agree there's niche websites that generate tonnes of money and have been around for years but nobody really knows about them... And the webmaster likes it that way
If you have a good idea you already have a lot of competition. Bad ideas have no competition because they are bad ideas that return every few years to fail again.
