Many drivers fall back to legacy writes to perform w:0 inserts since commands are acknowledged. During the 3.2 dev cycle, all operations are becoming available as commands, and we have introduced a new mechanism (OP_COMMAND) for issuing commands. Over the next few server releases, the non-OP_COMMAND mechanisms for communicating with the server will be deprecated and then removed. If we intend to continue to support un-ack'ed operations, we will need to extend OP_COMMAND (or invent a wholly new facility) to support these operations, and drivers will need to be updated to conform.