Issues with SQLite:

1. The test suite is not open source
2. External contributions are not welcomed
3. It's written in C, which is nowadays prone to easily-avoidable bugs, hard to maintain and add new features
4. SQLite does not support concurrent writes
5. Columns are weakly typed

Note the SQLite documentation hints Rust as a potential language for a rewrite under conditions listed at the end of the page.

Where Turso is good: scaling (instead of switching to PostgreSQL). Also it's simple to build an extension for it