I'm not sure 2015 counts as new, but that's same release that first introduced the JSON extension. There isn't a version of SQLite with JSON expressions but without indexes on expressions. Also, the JSON extension wasn't enabled by default until 2022, so most people using SQLite with JSON have got a version much newer than 2015.
> The ability to index expressions was added to SQLite with version 3.9.0 (2015-10-14).
So this is a relatively new addition to SQLite.