DBUS kded interface: Add newVault() and importVault() methods, which take all needed parameters from DBUS call. There should be a possibility to pass an empty string for default option, eg. encryption engine = CryFS when not specified. newVault() only shows a password window to collect the new password from user. Or (optionally) it can take password from DBUS call as well (would that be safe?)
This would be problematic since the backends have different options. What /could/ be possible is to have API that assumes all options have the default values - and only leaves device, mountPoint and backend. The password can not be passed in via dbus safely, so that part is definitely out :) Alternatively, there could be a plasma-vault-cli console app for doing this.