Inheritance / Polymorphism
Support for polymorphism would be a huge plus. In particular, being able to define a class structure and then query for a base class (or interface?) to get a list of all the various concrete classes.
Related GitHub Issue: https://github.com/realm/realm-java/issues/761
"Using an option type for polymorphic relationships" works pretty well.
I know this is on the roadmap for "Beyond August 2020", but I would like to see this as soon as possible. This is the biggest thing that is keeping us from using Realm.