Even if they had that kind of money just lying about, and were willing to throw it at a long term expansion project, would you throw it at PNG, or would you throw it at another market where you're likely to see a larger return in a much smaller timeframe?
Let's be honest, PNG still wouldn't be in the top five even if the NRL were inclined to go down that route. That money would be headed the way of Melbourne, Adelaide, NZ etc, maybe even somewhere more exotic, long before Port Moresby got a look in.