Thanks a lot for your input. We have proof of fairness on our roadmap. Currently we are using a non-deterministic algorithm, where results cannot be reproduced. Hence no proof of fairness, yet.
However I am not sure if we will use the steem blockchain (or any other blockchain) to generate the random number. Wouldn't it be technically possible for someone with enough comp power to predict the proof of work submissions in the short future, at least just sometimes? It wouldn't need to be 100%, just a small edge would be enough to win on the long term.