I actually think this is a poor idea. Part of the idea of directory
replicas (be they AD or OD) is that they are on physical machines in
different locations. This puts the login machines closer to the
clients that are actually using them. In fact, AD has the concept
of "sites" that allows the client to automatically prefer domain
controllers on the same subnet. Also, virtualizing a service does
not save you from a hardware problem. What happens if your box
running an OD master and 3 ODRs eats it? You have no OD replicas to
take over? Isn't that the point of a replica to begin with?
Of course, it does not obliterate the need for hardware redundancy.
But it is a good way to test if replicas work properly before
deployment.
