Buleprintable Components support PrimitiveComponents

Hey all!
I love the blueprintable component system, working like this really keeps my code base clean and modular.

I was wondering if it would be possible to extend classes i made in C++ in blueprints if they are derived from anything other then UActorComponent or USceneComponent?
For example, a UStaticMeshComponent or a UBoxComponent.
I have no problem extending them in C++, but i can not do the same with Blueprints.

Blueprintable components is no longer on the roadmap as far as i can see, is it feature complete?

Thank you!~