Sealed classes - would you want them in D? (v2)

[KingJoffrey]

I propose an idea, for discussion (robust discussion even better 
;-)

Add an new attribute to class, named 'sealed'.

No, not sealed as in Scala.

No, not sealed as in C#

sealed as in oxford dictionary (close securely, non-porous).

when sealed is applied on the class, this means the class is 
sealed.

the sealed attribute only makes sense within a module, and 
affects nothing outside of the module.

When sealed is applied to the class, then, interfacing to a class 
within a module, from code outside that class - but still within 
the module, can now only occur via the published interface of the 
class.

outside code in the module, can no longer directly access your 
private parts!

The class is sealed.