Currently, we can use the rs.syncFrom() helper to provide a temporary override on who we want a node to sync-off of. However, when performing an initial sync, either because of falling off the oplog or adding a node, we have no mechanism to do this.

The second we start up the server it will begin initial sync without a way for us who to determine whom we want to sync off of (without downtime). Potentially putting unwanted load on a primary or other node.

It would be nice to make syncFrom somehow determinable at startup time prior to the initial sync beginning.