There are updates of the proposal based on your feedback! The main change is that we moved from confusing 

T!!

 syntax to a limited version of intersection types – 

T & Any

. It’s likely that at some point we’ll have full support for intersection types and then it would be just a special case that doesn’t deserve special syntax because it seems that the only real-world use-case we have by now is overrides of annotated Java.

Oh wow this was honestly quite unexpected but very welcomed. Is there a possibility maybe just maybe please maybe to put a (very rudimentary and rough) version of intersection types behind an experimental flag? Because IIRC intersection types are already in the compiler and so having a rough user-facing version of them behind a flag shouldn't be too difficult.

Unfortunately, we don’t have any plans on intersection types for now. By the way, if you have some real-world use-cases for the feature, please file them to https://youtrack.jetbrains.com/