So I cannot figure out if this is a thing, but if not, I’m kinda confused why it’s not been brought up before.
If I share my server to a family member, only that account can see what I allow. But let’s say they have a child, who may want to view things on the Plex server, there isn’t an easy way of setting up restrictions for that child. It doesn’t make sense for a 4-year old to get an email address and create a Plex account for me to share to… or at least it doesn’t make sense in my world. 
So what about Shared Family accounts? I can share my server to my relative, allow them to create managed-sub-accounts. That way the relative signs into devices with their credentials, they can manage their family sub-accounts, their family can select their profile appropriately, and we don’t have a 4-year old watching Fifty Shades of Gray, they can watch Peppa Pig because that profile is only allowed to see certain libraries now. 
Does this make sense? Does it seem like a feature other folks can use?