One request I'd make in these discussions is that we avoid using the term "block" - it makes people think of the /dev/random behaviour (i.e. blocking intermittently and unhelpfully), rather than the usually-desired "wait for sufficient entropy on system startup" behaviour.

I'd also request that we keep in mind that any Linux user always remains free to write the 3-line utility function:

    def read_urandom(num_bytes):
        with open('/dev/urandom', 'rb') as urandom:
            return urandom.read(num_bytes)

If they want to get precisely the Linux /dev/urandom semantics, and not a Python level abstraction that provides the same kinds of assurances offered by other *nix platforms.