Having an identity system that more or less guarantees that each person can only hold one identity at a time would allow many things that would otherwise be vounerable to sybil attacks to be built.
The method i'm proposing relies on having meetings organized where people authenticate each other.
Let's call the code/procedure an identity contract.
It would work like this:
1. Register an name in the identity contract
2. Give your approximate positional data, this can be updated as you move around.
3. A few days before the date, participants in the contract are randomly grouped together based on location, and get invited to a channel to communicate a meeting point.
4. The people thus invited (maybe around 10-20 people, depending on how many are registered in this area) gather to the agreed upon meeting point.
5. At the meeting, each participant signs a statement saying who they met at the meeting, so that every person is signed by at least one other who was participating in this meetup.
6. The contract registers that the meeting was successful, and gives everyone involved one identity point.
This protocol relies on the fact that you cannot be in two places at once, and as long as you participate in a majority of your meetings, everyone can be sure that the identity you chose is your only identity within this system.
I have not been able to see any obvious attacks on this system, but maybe i'm missing out on something? Would love to hear your comments.