Unfortunately one of the requirements of a good identity system is that it should keep personal data secret from parties who do not need it. This means that blockchains on their own aren't a good fit, since by design they share all information with all parties.
Having said that, BrightID uses a blockchain and seems like an idea worth exploring.
Having said that, BrightID uses a blockchain and seems like an idea worth exploring.
https://www.brightid.org/whitepaper