You mention wanting to do a Go version. Not sure if it's useful, but this is a SQLite "bulk data generation" util I threw together ages ago in Go:

https://github.com/sqlitebrowser/sqlitedatagen

There's some initial work to parallelise it with goroutines here:

https://github.com/sqlitebrowser/sqlitedatagen/blob/multi_ro...

Didn't go very far down that track though, as the mostly single threaded nature of writes in SQLite seemed to prevent that from really achieving much. Well, I _think_ that's why it didn't really help. ;)