Any form of PoS will inherently benefit the most for those with the biggest pile of coins.  It was bit of an eye opener for me, but actually any form of interest is debt based: The whole point of the banks is that they offer interest over money so that they can make more profit on loans. Even without the actual loan on the other side counter balancing the interest rate, PoS will put pressure on the market and decrease a coins value. You can actually see this happening in large with MintCoin and ZeitCoin which have a huge PoS reward.

A form of decentralised Proof of Coop (PoC?) is more towards a human process to acknowledge the cooperation you have done with a reward. The model needs to be simple as well as uncrackable w/o the need to bring out a new piece of software whenever a trusted node (read human) is added, removed or disappears (for health or trust reasons). The biggest challenge will be that people (we possibly even may trust) will try game the system and we need to be prepared for that.

Last but not least; I'm not sure if we should completely get rid of PoS, since it's a fairly cheap way to generate transactions which secure the network. We may want to just trim down the pos reward to the bare minimum or a fixed value just as we're doing now with PoW.

@smartaction; I'm looking forward to the complete whitepaper.