Sure, but note that your usecase goes specifically against fhs and posix specs:
>Programs must not assume that any files or directories in /tmp are preserved between invocations of the program.
>Although data stored in /tmp may be deleted in a site-specific manner, it is recommended that files and directories located in /tmp be deleted whenever the system is booted.
Now you can obviously use your Filesystem whichever way you like, but I would say Debian shouldn't have to take into consideration uses which are outside the general recommendations/specs.
The user wasn't "advising" this, or asking if it was fine. They're just doing it. Everything that they want to do with their own computer is permissible.
The person you're replying to is saying that tmp is meant for temporary storage that could disappear between reboots. A permanent archive of the past states of the tmp directory is not temporary.
>Programs must not assume that any files or directories in /tmp are preserved between invocations of the program.
>Although data stored in /tmp may be deleted in a site-specific manner, it is recommended that files and directories located in /tmp be deleted whenever the system is booted.
https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch03s18.htm...
Now you can obviously use your Filesystem whichever way you like, but I would say Debian shouldn't have to take into consideration uses which are outside the general recommendations/specs.