zero knowledge proofs, like those being deployed on blockchains recently, have the potential to be the killer app for this tech. Imagine you want a library card which requires proof of residence. With a zero-proof identity system, you could get your library card without revealing any personal info, like your name or address. Your wallets would simply prove to the library that you are a resident as credentialed by some local/state authority.

This also could have profound implications for the web like universal logins to web services, online privacy while still providing attribution, ownership and rights to digital content, copyright, etc.