Would the thinking be different if the question were phrased as:
Assign a topic/message to multiple users at the same time?
Very often we have a single request that needs to be handled independently by multiple people. (e.g., Persons X, Y, and Z need to do code review; team members A, B, C, and D all need to summarize their user interviews.)
Otherwise, we have to create parallel topics for the same request, to accomodate each assignee, which seems noisy.