I also wrote on the "diminishing returns" algo well over a year ago. It remains my favourite method as is easy to encode on the blockchain. I did have discussions with SteemitInc at the time but it went nowhere as was considered too computationally costly.

I also did some work on vote-rings and it is mathematically possible to distinguish such rings from, say, a group of friends. In this case, it requires some "sentinels" to "search and destroy"; unfortunately the "destroy" part is limited to downvoting, which is wasteful and ineffective. As Vitalik mentioned about this, that the penalty must be greater than the gain, else it is not a deterrent and is seen as a small tax on income.