As it stands, TicketReminderPlugin is the last plugin I'm using in my production server that doesn't have a Python 3 solution. This is a fairly large plugin, but I use the capabilities for users to change their passwords, as well as to be able to create accounts and reset passwords.
I was hoping / expecting that someone might be working on this plugin, which is why I left it for last. However, I haven't seen activity on it, so I ended up starting the process myself. I got through the generic Python 3 mods, made a rough draft of some of the templates, and got the password change feature working in preferences (using digest authentication). The Notification panel seems to show up OK, and the top part of the Users panel. However, the pagination area is not implemented. As of yet, I have not tackled something quite like that and I'll have to spend time investigating how to do it.
I just mention this in case someone else is working on this plugin. I would be happy to wait a while for an update if someone else is spending time on it, or to provide my partial solution if someone wants to pick it up. If I don't hear from anyone, I'll probably just keep working on it as time allows, FWIW.