Currently, GroupRequest is optimized towards invoking group RPCs. If we invoke an RPC on a single destination (versus a group), we incure overhead. For example, the target destination is wrapped into a list, and we acquire locks to modify the target list on SUSPECT and VIEW_CHANGE events.
Goal: to create a SingleDestinationRequest, which has only 1 target destination address. For unicast RPCs, this should be much more efficient