The ability to rollback "bad" transactions would be key in being able to comply with legal requirements, resolve contract disputes, etc. Plus having Sybil proof

The ability to rollback "bad" transactions would be key in being able to comply with legal requirements, resolve contract disputes, etc. Plus having Sybil proof systems require PoW or PoS both of which could be difficult and inefficient for a market specific solution. E.g. why would people want to run a miner for pork chop trading? PoS might work though but still requires a founding core group that's trusted IMHO.