Deploying replication topologies would be far simpler for end-users if they didn't have to worry about the distinction between DS and RS instances. The goal of this issue is to simplify deployment by combining the two roles: all DJ instances will have both DS and RS roles.
RSs are fully connected so WAN traffic between data centers will increase dramatically once the two roles are merged. Therefore, it is absolutely necessary to implement a more intelligent routing mechanism before embarking on this issue, see OPENDJ-4925.
This issue will probably need to be split up a bit at the start of the 7.0 dev cycle.