[stigmata]

It's a great idea.

There is potenially an easy way to get round the trust problem: Only trade variance on hands mined by a trusted 3rd party (e.g. HSDB). This means only one party (the miner) really needs to be trusted. If he is taking a small cut for organisation, then there is a strong pressure to stay honest & trusted.

It could have some problems (need close to full coverage, need to trust the dataminer), but it should be the simplest implementation, and means that everyone is free to sign up, even complete unknowns.