I've been thinking about something like this for decentralized location sharing... It would probably be a custom "kind" but you would have your phone post an encrypted geohash to relays, with a level of precision defined by whomever you wanted to see it.
For instance you could just share "city-level" details with certain people ... Allow you to know if someone's "in town".
Or with more select people you share exact location
Phone posts it periodically to relays as a custom kind
