Very good post @Al_Kafir. I’ll jump right in to say I think the 1 vault SafeCoin = 1 vote won’t work as things stand, and the problem (anyone can run multiple vaults - eg in the cloud - if they can pay for them) will be hard to fix in this model. So I think a proof of unique human is what’s really needed, or something that gets us as close to that as possible.
I do like the principle of tying together uniqueness and contributing: 1 unique human farmer = 1 vote and your scheme of linking this to SafeCoin creates a minimum threshold which is good too. There’s an issue though when it becomes very expensive to farm a SafeCoin (ie as SafeCoin itself becomes more valuable), because again it means wealthy farmers get votes more easily.
So I think those are the key issues to be solved here, along with making it hard to trade votes.
I don’t have any solutions at this point, but maybe there are other schemes and theories that can be borrowed or adapted. I don’t know and haven’t thought much about it but there must be lots of research and theory on this kind of thing, as well as the other efforts in the crypto sphere. It’s a hard problem though.