It will be perfect, if users will be able to protect sensitive data with the second password (not re prompting master password). The master password decrypt full storage and it will very good story, if your sensitive information, like secret words from crypto wallet or bank information will stay encrypted with another one password, while storage is open. I mean your data will encrypted two times, by your master password and the second one password.
It can be implemented as encrypted folders more common way or as option for entity (password, note, card, folder and etc.).
I believe it not a very difficult for implementation, but it will be very nice to have it.
Thanks.