For one thing, they're ripping it out because of its poor write parallelism
https://youtu.be/nlus1Z7TVTI?t=271But that's orthogonal to my point. As a user of FoundationDB, you're not programming directly against SQLite, so you aren't going to run into these issues as much since FoundationDB exposes different semantics and coordinates concurrency across many SQLite instances in parallel.
I think it's best to think of SQLite as a replacement for your filesystem, rather than a replacement for your relational DBMS.