There’s been a few feature requests for custom recommendations, but I believe you can cover nearly all needs by implementing a Recommendation Builder Tool.
I envision a section in library management where you can build custom recommendations based on dynamic metadata filters (e.g., (movie = unwatched) AND (genre = Sci-Fi OR genre = Horror)).
These recommendations would then be listed as an option under Library Management today where they can be applied to Library Recommended, Home, and Friends’ Home.
With these rule-based recommendations, users can fully customize their PLEX experience and make it their own.