Here is my practice (I use only darktable for photo management and have no working solution what to do with images I work on in other editors such as gimp or hugin):
For tagging people I use the quicktag lua script to attach shortcuts to tags:
For each film roll I usually have to tag less than ten different people frequently so the ones that I expect to tag most often get shortcuts. There are still some features that would be handy, such as a possibility to save shortcut sets and an shortcut overlay mode that can reuse shortcuts that are already used in darktable.
Copy-attach-detach-tags comes handy as well, for copy and paste of tags I use just the keys “c” and “v”. This helps a lot with sequences of similar images.
The tag structure that works best for me is
I have the special tag
People|? if not all people in the image are known, e.g. colleagues of my wife where I only know the first name and have to ask her for the full name later. I decide on a per picture basis whom on the picture to tag and whom to consider unimportant (e.g. passersby).
Unfortunately there is no automatic way to tell how many pictures are left untouched in terms of people tagging. I always think about implementing something in lua that can help to assess the tagging status of a film roll, but at the moment I have a simple spread sheet where I denote for each film roll the status of “people tagged”, “places tagged” (as tags, scheme
Places|Country|State|City|Place but each being optional, e.g. omitting the country in my home country) and geotags added with the options “not done”, “started” and “done whole roll”.