It does indeed turn out to be a difficult and subtle problem. We've tried to balance minimizing novelty (always risky in cryptographic systems) with achieving the various security and scaling properties we're looking for. We're very lucky at Ink & Switch to be working with Brooke Zelenka on this one.
On further review this is quite a lot further developed than what I suggested above. Sorry for the noise!
It does indeed turn out to be a difficult and subtle problem. We've tried to balance minimizing novelty (always risky in cryptographic systems) with achieving the various security and scaling properties we're looking for. We're very lucky at Ink & Switch to be working with Brooke Zelenka on this one.