Hi,
I wanted to post about this since no one else has, as far as I searched. The ability to erase all type of files and photos with 3, 7 or even 35 passes?
Selecting anything from your gallery or explorer will have the option to do that maybe?
This might hot up the phone and drain it’s battery life and shorten it’s life span. I wouldn’t know but would this be a possible feature added to the phone? 
The thing exists and is called scrub. Making multiple passes is sensible for magnetic media, where you can read it in higher resolution then standard head provides, and recover old data from track edges (disk heads never go exactly the same way). Can’t tell if it’s possible to read former states from solid state storage.
I think this was implied in the previous post, but one should only use those utilities on magnetic drives. SSDs and USB storage have writing limits. With wear-leveling, the old data might remain anyway as the file location may not be overwritten. It may move.
SSDs have an option to ‘trim’. At one time, I saw posts in this forum stating that it had been disabled for certain SSDs on Librems, but I do not know if that is still true. Someone more knowlegable can say how to check.
UPDATE: Here is the link to the other thread. There has been no recent update, but PureOS does not seem to have trimming per Mladen’s instructions.