It's an interesting thought. Any online brokerage, lender or retail banker could probably set up an anonymous verification of asset ownership without going through background checks or credit agencies. You just need 2-party consent and verification, not a whole blockchain. The trick is not proving you own a thing, it's that you need to prove you haven't used it as collateral for anyone else or don't hold outstanding debts somewhere else. Blockchain will be completely useless for solving that. A universal identity (ie SSN) is the only option.