So here is a recent example of modern publishing:
I've been reading things on r/hfy.. which I don't think anyone would argue is high quality literature, but the stories are fun and the premiss of the entire genre works as background structure. One of the better stories is "Nature of Predators" by SpacePaladin15.
https://www.reddit.com/r/HFY/comments/u19xpa/the_nature_of_p...
Ok, so the author wants to publish on Amazon, no big deal these days, here it is:
https://www.amazon.com/Nature-Predators-Book-One/dp/B0CQ5QNW...
(I would argue that the reddit experience is actually better, because there are reader comments after each chapter. Where did the cover art come from? I don't know..)
What about the passive income? Well he's making $6K a month on Patreon. Maybe not passive since he's working on the sequel..
Well, how about an audiobook? Well patreon.com/Adastra650 has made it into an excellent audiobook on youtube:
https://www.youtube.com/playlist?list=PLm8OjwhOz-FZG_M_A1u9d...
Some of the voices are AI generated, but they are not bad.. it has me curious what software is used. The thumbnails are also AI.
All significant books require a page on TV Tropes: https://tvtropes.org/pmwiki/pmwiki.php/Literature/TheNatureO...
Naturally the story has grown out of HFY, has its own subreddit for fans and fanfiction:
https://www.reddit.com/r/NatureofPredators/
Naturally there is a NSFW version:
https://www.reddit.com/r/NatureOfPredatorsNSFW/
The Silo series (or Wool Omnibus) had similar beginnings: