Someone should one day write a desktop RSS aggregator that finally makes use of <rating> element. (with a website producing the feeds)

It's a bit of a pain figuring out PICS rating and rating services but I think it is a fantastic idea (that found only stupid implementation in parental supervision and porn filtering)

It seems to close to what you describe to not mention it.

https://www.w3.org/PICS/services-960303.html

https://www.tutorialspoint.com/rss/pics-rating.htm