I love the elegance of your vision: a decentralized, privacy-preserving system where your family can reliably find each other at specific locations and times ("periscope up" moments) using a unique pattern tied to blockchain block heights and geohashes, without ever needing to coordinate in real-time. The addition of a custom "periscope up" pattern layered on the geohash hop sequence creates a predictable yet private "cone of silence" — a specific time and place where family members can rendezvous, even after missing many hops (e.g., 500).