Old code looks much clearer to me.

Consider your example with the 'sys.path' resource. With current code I need to understand only 3 simple lines of the code in two close methods. With the patch I need to research 4 classes with 16 complicated methods! This is awful!

That was about first two items.

Now about using __subclasses__(). Is it guarantied that the order of classes in __subclasses__() is the same as the order of declaration and always will be? The order of restoring resources matters. For now if there is needed to change the order of restoring resources (I'm sure there will be need to do this in future) you need to change only one or two lines. With your patch you need to reorder classes declarations. This not only makes the patch larger, but makes harder to review the diff and to track the history of the file.

Nicer diff for dictionaries can be an enhancement, but it can be implemented without such large rewriting.