That would make memory management more automatic and allow sharing objects more
easily.

Beware of the following situation :
obj->updated.connect (sigc::bind (sigc::mem_fun (this,
&Foo::Bar::on_obj_updated), obj);

this makes obj store a reference to itself -- it will get released when the
Foo::Bar objects gets freed (if it's a sigc::trackable), but will be kept
otherwise, which may not be intended.