I'd like to see a fork of SQLite that "supports the PostgreSQL wire protocol and the majority of PostgreSQL syntax" (to quote another popular db).
Postgres has foreign data wrappers which can kinda achieve this(see also: https://github.com/pgspider/sqlite_fdw ), but ive been surprised by how well sqlite is already supported by many tools : sometimes it comes for free as its used in testing - hooking up stuff like litestream can work really wel l too