We propose a scalable self-sovereign identity (S3I) system architecture that uses a hierarchically structured Byzantine fault tolerance layer of validating authorities and a permissioned blockchain to record and manage user identities. Users and service providers interact with the S3I system through nearby proxy nodes that store copies of the blockchain but do not participate in the consensus protocol. We identify different challenges of such a system and discuss design choices that allow those challenges to be addressed and ultimately resolved, with focus on networking issues such as performance and coverage. We also show preliminary performance evaluation results that confirm the validity of the proposed approach.