There are certain scenarios where priority takeover never succeeds. For example, if a user has 3 nodes in the main datacenter and 2 nodes in the backup datacenter. They want to move the primary from the main datacenter to the backup datacenter, so they raise the priority of a node in the backup datacenter. However, the nodes in the backup datacenter are always behind the main datacenter, so they can never win an election.

A proposed fix to this is to let replSetStepDown accept a suggested next primary. When the command waits for a majority of nodes to catch up, it also waits for the suggested next primary to catch up. It then sends the replSetStepUp command to the suggested next primary.