"Actors are reference types, but why classes?"

[DevAndArtist (Adrian Meister)]

A possible alternative way for actor extensibility to cover some (but not all) use cases:

Is there possible to support inheriting from a generic type: class classA<T: classB>: T?

I think an associated-objects-like "stored properties in extensions" feature would be significantly more interesting and feasible than doing a whole mess of design and implementation work around allowing generic subclassing.