I think more useful would be to be able to boot into another data partition with a different password, which, in turn, would hide the other "daily" partition. I believe LUKS is capable of that. The storage dump looks like a random set of data and only a valid password can find and decrypt a matching hidden partition.
Ideally this should also work on lock screen, e.g. if you type in a non-standard PIN, it would boot from the "dummy" partition in the background, with a slight delay perhaps.
This way you don't have backup anything (I mean you should, but for normal purposes) and have a plausible deniability whenever you get randomly inspected, not just at border crossings that you anticipate.
Not possible to have a robust implementation with the current tech unfortunately.
That isn't truly hidden and can be detected as a low level from the SSD.
Having different data partition forces you to hide stuff, which can be unlawful in some juridictions.
Not having the data in the first place in some specific contexts (like crossing borders) is easier.
>I believe LUKS is capable of that
Booting into a 30 GB partition on a 128GB phone is going to be mega suspicious, even if the remaining data is random.