One important point here: In the article the author says that the location of the database is /sdcard/WhatsApp/Databases. That's not entirely correct.
It only gets copied there when you use the build in backup feature (Settings -> Chat Settings). Else, it sits "safely" under /data/data/com.whatsapp/databases like every other Android sqlite database.
But nonetheless, WhatsApp was and is not really known for its safety...
This needs to be at the top. The fix here is very simple then - prompt the user for a passphrase when doing a backup, allow no passphrase for a "friction free" if you really want to, but give the user the option.
It only gets copied there when you use the build in backup feature (Settings -> Chat Settings). Else, it sits "safely" under /data/data/com.whatsapp/databases like every other Android sqlite database.
But nonetheless, WhatsApp was and is not really known for its safety...