Wouldn't processes on same machine be able to use different IPCs that don't even touch file ? It's neat but I have feeling in vast majority of cases just passing address to one of the IPC methods would be faster and then SQLite itself would only be needed for the durable parts.

This extension piggyback SQLite native transactions. For example, queueing data will be rolled back if transaction is rolled back due to some constrains violations.

It is possible to achieve with external IPC, but require a lot of very careful programming.