Well, it does work out. In his third article on optional static type declarations for Python, Guido van Rossum addresses all the comments and presents what I think is a compact and sensible proposal. Interfaces are a useful mechanism for stricter duck-typing - of course optional, so only where you need it. And automatic type adaptation is a good idea - it's about time that PEP 246 gets integrated into Python.
But the most important thing remains: it's optional. Whoever doesn't need it can leave it out.