I am wondering if there are any plans, either in the near or distant future, to ever add synchronization support for arbitrary objects.  The interface could be simple, every class takes one additional template argument, the class name of a locking object which defaults to some class that provides stub methods so that by default all classes are unsychronized.  Then, if I want my object to become synchronized, I can pass it whatever type of lock I deem appropriate.  Of course any object can be synchronized currently by making a class that exposes the same interface and acquires a lock before forwarding to the internal boost implementation, but this is inefficient, as the internal details of the object’s implementation are not always such that an entire method needs to be locked.  Perhaps only a single line of code inside a long method needs to be locked. 

Has this ever been considered in the past?