It sounds like ZeroCoin v2 eliminates one major criticism, that of bloat.

But engineering hurdles remain:

• 1. Requires a hard fork
• 2. Any requirement that all transactions participate in mixing is a non-starter.  Some payment schemes bootstrap trust by intentionally being non-private, showing their bitcoin holdings and bitcoin payments with provable digital signatures.

Any forced 100% privacy scheme that prevented opt-in auditing would make life difficult for some existing users, who place value in the transparency of the system.

I would rather see automatic mixing and privacy built into every client.