Of ≈17 million Chinese students who graduated junior high school after grade 9 in 2024, ≈10 million were admitted to a high school, ≈4 million to a vocational school and the remaining ≈3 million disappear from education statistics, presumably directly entering the workforce. http://www.moe.gov.cn/jyb_sjzl/sjzl_fztjgb/202506/t20250611_...

So at least in theory there's still lots of room to increase high school enrollment, though I doubt this would lead to noticeably more geniuses. The testing system is pretty good at sorting the best students into good schools, I think.