As long as the reference Keccak code is going to live in the python stdlib anyway, I would /greatly/ appreciate it if the Keccak sponge function was directly exposed instead of just the fixed parameters used for SHA-3. 

A Keccak sponge can have a much wider range of rates/capacities, and after absorption can have any number of bytes squeezed out. The ability to get an unbounded number of bytes out is very useful and I've written some code that uses that behavior. I ended up having to write my own Keccak python library since none of the other SHA-3 libraries exposed this either.