I'm feeling uncomfortable about this. I think that small stakeholders should be able to have a good chance to mine, as well as a good incentive to keep their nodes up and running.
As I understand it, the only way to earn stake now is to mine a block with one of your own transactions in it.... a transaction which destroys your own CD. So for a small stakeholder, it's a one-shot deal; you save up your CD, then make a transaction (could be back to yourself), and hope that the CDD earns you the block.
I propose a second metric, Stake Days Destroyed, to go along with CDD. This would also impact the Difficulty. As SDD goes up, difficulty goes down. If I hold 30 shares for 30 days, my SDD is 900. This is the equivalent of somebody with 900 shares holding for 1 day. The key part is this: My SDD only drops back to 0 when I actually mine a block. The SDD essentially help the smaller guys "cut in line" by being able to mine easier when they have been saving up their Stake for a long time. And since Stake is only reset to 0 when a block is mined, it can be transferred from one address to another without being reset. The stake travels along with the shares and can be additive. If I've got 0 stake (I just mined a block with my shares) but I buy shares from you, and your shares have stake built up, I receive that stake when I receive the shares, and my chances of mining a block go up again.
I don't know, I just feel that fundamentally, PoS mining should not result in the large stakeholders getting ALL of the blocks. The chances should be proportional to the stake held by each. If I own 1/100,000 of the shares, I should have a 1/100,000 chance of mining a block (unless I do something to ruin my chances somehow, such as not allowing my stake to mature or whatever).
I get the idea of TaPoS as encouraging transactions rather than sitting on shares and never trading with them. But if the only way to earn PoS is to save up your CD for the big shot transaction which is likely to win a block, and to conduct that transaction once per year, this will incentivize perverse behavior as well. Just leave your client off most of the time, fire it up once per year, make a transaction from one address to another, and then turn it off until next year. Doing basically nothing to secure the network.
We want to incentivize making transactions, and also incentivize having client nodes running and mining. I feel like the system as presently described (as well as I understand it, which granted is not fully) does not incentivize the little guys to mine, which leads to concentration/centralization of mining power, which is exactly what we're trying to get away from by moving from PoW to PoS.
EDIT: To elaborate a little more. Stake is associated only with the shares, not the shareholder. If I have 2 shares, I mine a block, they now have 0 stake-days, their stake-days start to build up. If you transfer to me 2 shares, that have not mined a block in 5 days, they now have 10 stake-days (5 each). Now I have 4 shares, 2 of which have 0 stake-days, and 2 of which have 10 stake-days. If I send them all 4 at once, they can act as though there are 10 stake-days destroyed as part of that transaction. Or if I send 1 share to somebody else, I have to pick whether I want to send a 0-stake-day share or a 5-stake-day share. The system will, by default, keep my highest stake-day shares and send the lowest stake-day shares.
Even when my stake-days have built up, I am not incentivized to spam the blockchain with transactions sending shares back-and-forth from one address to another in hopes of mining a block, because the CDD still contributes the difficulty, and very small CDD will make the difficulty pretty high. I am not proposing to eliminate CDD, only augment it with a parallel system that works similarly.