There’s already existing feature suggestions discussing this to some degree.
e.g. one specifically asking for more content rating information and an option to add (or link) the IMDb parental guide. There’s a few similar ones asking for the same kind of information from different sources like Common Sense Media or Kids in Mind.
There’s also a suggestion discussing support for keywords and importing of keywords from TMDb. As for restricting libraries… there’s already Sharing Labels in Plex to use for that.
