It would be nice to have a mode where all the system files are on the built in storage, but any user data, like passwords, keys, recordings, are stored on the SD with with or without some sort of encryption.
The basic point is that a mode where all user data goes to the SD card automatically without needing to be told or asked where it should go.
Perhaps a Normal mode, a mode to store user data on SD, and a mode that keeps redundant copies on the built in storage and the SD card.