It could be part of it, but we at least need need something where we can post our public keys in a credible way, and then for these to be linked to our identity. You are right to define the difference between making our public keys discoverable and the trustworthiness our identity, and eventually they should be linked in some way. In the end a great deal will depend on the trustworthiness of those validating our identity and in proving our claims, and this could exist on or off the blockchain.