Currently, the subdirs attribute of filecmp.dircmp does not respect subclassing:

>>> from filecmp import dircmp
>>> class MyDirCmp(dircmp):
...   pass
... 
>>> my_dcmp = MyDirCmp('dir1', 'dir2')
>>> for item in my_dcmp.subdirs.values():
...   print(type(item))
...   break
... 
<class 'filecmp.dircmp'>

This is the only place where dircmp does not respect subclassing.  It can be corrected here:

def phase4(self): # Find out differences between common subdirectories
    ...
        ...
        self.subdirs[x]  = dircmp(a_x, b_x, self.ignore, self.hide)

This would let one do things like override dircmp.report() and have dircmp.report_full_closure() behave as expected.