Group rides are one of the best features of Zwift but now that some are getting very big numbers of riders joining there are problems for the ride leaders keeping groups together. I suggest that the ride leader can assign the lantern rouge to a volunteer, someone who would be a sweep just now in a well organised ride.
This would define the rear of the group and assist the ride leader with organisation It could also be a deputy leader should the primary leader have a technical or not be able to join. The LR would have a red beam instead of yellow and would show up on the profile markers in red making it much easier to stay with a group
This is not a new idea and similar suggestions going all the way back to the start of group rides, the yellow beacon great and is improved now we can see all the messages but there is still frustration with riders off the front and sweepers trying to help riders at the rear. A Lantern Rouge would give definition to the group