Scary, yes but it could have an interesting positive outcome for others elsewhere.
Firstly, if the fish are causing as much damage as is being reported to the local ecology, then the local government has to act in some way. Imagine if this was back here and the invasive species was topmouth gudgeon or Japanese Knotweed to name a couple of current threats we currently face. For both of these, we are looking at several ways of tackling them including, with Japanese Knotweed, the release of Japanese bugs that feed exclusively on the Japanese Knotweed. How is this any different to the Australian government releasing KHV?
Secondly, I am pretty sure that when there have been outbreaks here of KHV, there have been survivors of the virus, just like there have been survivors of ebola in Africa. The net effect of this could result in a population of Carp that is immune to KHV, purely down to the numbers involved. This population could then be a source population that we could use to populate local waters with KHV resistant fish. Not what the Australian government intends or wants, but look at what's happening with anti-biotics.