It doesn't need to be Christmas Island. If you can maintain quarantine there you can do the same in one of the capital cities.Welcome to Christmas Island
I don't think there is an international airport on the island so there would have to be transfers made to and from the island which just increases the chances of getting the virus spread.
The only real problem has been the guards in Victoria doing the wrong thing. If they tighten this up, then it should be OK.