After the rather controversial decision of removing the last seen information, I would like to request having a "last action" field.
[...] I personally wouldn't mind a "last active" field which refers to my last public action (a post, a comment, a revision...)
I believe it to be a very good compromise because the last action a user has made is already public. One could open a profile, and rummage through posts, comments, votes, and see the last action, but it would take time.
So having it readily available would both save time for people moderating posts as well as respect the privacy concern of the users happy with the field disappearing.
To reiterate: this is not a request to add information that is not already available, simply to save time for the humans who use that information in the course of their moderation activities.