smxi does that but can only do it if you always use smxi, otherwise there's no actual way to know when a full upgrade has been run.
Remember that all upgrade/dist-upgrade means as far as I know (and correct me if I am wrong) is that you tell the system to install latest version of all the packages.
I have some understanding of the issues from making the smxi last upgrade thing, but that one only works if
a: you always use smxi to upgrade
b: the system has been upgraded by smxi before
the hack I did there was to simply add a 'last-upgrade=' item to the smxi.conf file, which smxi reads.
However, in the context of inxi, I do not know of any way to know the system has been upgraded or when, and such a feature should include at least rpm/deb, maybe pacman, though I doubt pacman has a way to know such things.
With this said, if you can find a way to actually determine when the system last was upgraded, let me know, I am failrly familiar with debian upgrade stuff and I could not find a way that a script could read from the system state itself.
Remember that to actually be a real upgrade, the system must not exit the upgrade before it's done, that's why smxi for example only sets the last upgrade time after du/upgrade exits/completes without error or user initiated exit.
as good as apt is, it's missing a few things, meaningful error return numbers for example, a flag set each fully completed upgrade, and some other basic stuff that would not be that hard to do in apt, but I don't believe they are done.
