Unless something unforeseeable happens the next three teams should come from Perth, NZ, and Adelaide in no particular order.
Anything else is taking the piss and a dereliction of the NRL's responsibilities to the game. If that doesn't happen they should just give it up, admit that they have no interest in being a national product and don't care about the sport's health outside of NSW and Qld, and allow us all to move on with our own plans.
I would be surprised if they are the next three sides.
At this point in time they will probably go with this crazy PNG idea as the next side.