Sounds like a generic form of single table inheritance. I don't honestly see any other way to do it (punting to a JSON field is effectively the same thing) when

Sounds like a generic form of single table inheritance. I don't honestly see any other way to do it (punting to a JSON field is effectively the same thing) when you have potentially thousands of parts all with their own super specific relevant attributes. I've worked on multiple products that have had a concept of "custom fields" who did it this way too.