TypeInfo: how much breakage?

[Andrei Alexandrescu]

The new TypeInfo design offers some interesting opportunities. Some of 
them are possible if we break some of the existing compatibility. The 
documented types are:

TypeInfo: https://dlang.org/library/object/type_info.html

TypeInfo_Class: https://dlang.org/library/object/type_info__class.html

I wonder to what extent people are using other undocumented derivatives 
of TypeInfo such as TypeInfo_Struct.