Andreas: I would prefer to avoid a dependency on the ipaddress module.  I would suggest adding an address_family constructor argument that defaults to None, where a value of None would mean "just pass the server_address to bind (or getaddrinfo?) and find out what the resulting family is".  I'm not exactly a socket programming expert, though, so there may be a reason I'm not aware of that that won't work well.

Carlos: no, this is a new feature, so it can go into 3.5 only at this point.