I just want to point out the point of an autosave.
That is, to protect users in the case of a crash.
Many crashes impact the entire system (eg, power loss, catastrophic overheat, angry chainsaw attack). That is a problem. However, autosave ensures that you don’t lose much work. Even if you don’t save often (easy to do if you don’t have the right habits), you won’t lose a ton of work.
By saving to /tmp/, blender is making its autosave worse than useless at protecting data loss from total system crashes. I work with a graphics card that sometimes dies without warning. I know that blender has an autosave, and so I set my interval to be low and expected it to work without me needing to save frequently. When my card recently went down, I restarted my computer, expecting Blender to have autosaved. Except that, because of this issue, the autosave had been deleted. It only served to lure me into a false sense of security.
This problem has a ridiculously simple solution. Save to /var/tmp instead of /tmp. /var/tmp files are persistent through shutdowns, but are still allowed to be cleaned. This change would only help: there is no situation in which it hurts the user. It would literally take less time for someone to change the destination directory to /var/tmp than it would for someone else to write about why it is the responsibility of the user to change this folder every time they boot up.