Hi, i would like to introduce an approach we are (XDN-project dev team) going to implement on the top of DigitalNote XDN blockchain http://digitalnote.org & http://digitalnote.org/whitepaper.
1. We want to implement PoA in XDN, rather than PeerCoin PoS, because we consider PoA is safer. It is truly HYBRID protocol: we need both PoW and PoS elements to produce a block, so 51% attack is harder. Remember, XDN has an ASIC-resistant proof-of-work.
2. Original protocol doesn't suit for an anonymous CryptoNote transactions. So we had 2 options:
2.1. Research and develop the new PoA scheme for XDN. That is a long and unpredictable way.
2.2. Implement a useful blockchain based feature (called deposits) and then apply the PoA based on blockchain deposits. So we chose it and made blockchain deposits based on multi-sigs a part of DigitalNote XDN.
3. Now we have deposits (check https://github.com/xdn-project/digitalnote), now we are ready to implement Proof-of-activity. Before that we want to discuss PoA with all interested parties.
4. Also we noticed a possible problem with the original PoA. ONLY the "last" "stakeholder" can set transactions for a new block. When done, he signs and broadcasts a new block to the network. Seems nothing wrong here, but "last" "stakeholder" can produce as many valid blocks as he needs by changing transactions set. So he can split the blockchain and make a double spend. In that case we are planning to give a right of setting up a block to the Proof-of-work miners.