Ok, I think I now have a system to force photoanalysisd to kick in, thanks to help from you fine folks - basically, force the Mac to be as idle as possible and then it kicks in:
Before I leave my Mac for the night:
- quit all Mac apps
- reboot, make sure no apps are running
- open Photos, then quit Photos
Then we play the waiting game, and usually within an hour it seems to kick in. Screenshot is what I saw this morning, and I've already noticed more faces found. Also THIS IS RIDICULOUS.