This really is quite incredible. Same idea extends to your filesystem too. Tracking millions of 1KB objects on disk? You could load the whole set into memory substantially faster from SQLite using the same disk. If WAL is enabled with reasonable sync flags, the same applies going back out to disk as well.
SQLite is the most powerful dependency that our product uses today. We have been using it in production as the sole persistence mechanism for 100% of our data for the last 5-6 years now. Recently, we have started leveraging the actual SQL engine to process all of our business logic as well.