I think it's the difference between eulogy and obituary; one is designed to arouse emotion, the other to inform. The question is: does the first vs. last name

I think it's the difference between eulogy and obituary; one is designed to arouse emotion, the other to inform. The question is: does the first vs. last name convention tie to the speaker (typically eulogy will be written by one who knew them, obituary likely not) or to the listeners. I'd suggest the latter, the same way a priest who didn't know the dead person would give the eulogy as if he knew them, because he is talking to their friends and family. If 30 years after your death I were to write about your work then I would probably use full name or last name, whereas if someone asked "was he friendly on HN" then forename might be more appropriate?