One to investigate once the main functions are good.....
The option to share your location with a group (Event attendees would be good).
I get the inspiration for this from the 'ViewRanger' walkers navigation app.
Options to send position once or at regular intervals and to monitor the position of others in the group.
I have found riding in a "GPS convoy" where all in a group are following the same shared route but don't need to stay in sight contact to be very effective.
Possibly generating an alert when one of the group goes off route or stops for longer than X minutes.