Harry Potter was a smash hit about a boy discovering he’s a wizard and going to school in a magical world full of wonder and adventure. Twilight didn’t hit quite that high a note, but the story of a teenage girl who learns her classmate is a vampire and falls in love with him did quite well. The Hunger Games popularized the dystopian genre with a bow wielding teenager stepping up to survive death games, have angsty romances, and fight the power.
As far as I can tell, nothing has quite hit that same kind of high since and it may be awhile until the next truly big wave. But if it were up to you, what would the next big thing be about?
YA copies adult trends. If the adult trend is waning or too similar, like parallel universes (MCU has oversaturated the market), it will switch to an older trend that’s fallen out of fashion. Harry Potter wasn’t successful because of magic kid, that’s been a thing for decades, but because it’s part of the British boarding school genre popular 100 years ago. Take something forgotten, add a new spin on it, and you have your next big thing.
It’s not all recycled content. One way to make newish stories is to take a scifi idea and make it kid friendly, like posthumans or generation ships. It doesn’t matter if it’s “been done before”, it’s not about being first, it’s what captures the imagination (and sells).