I think the top 3 will change. In fact if you rated the countries where RL had the most fans PNG would already be in the top 3 ahead of NZ. As for playing ability, Samoa and Tonga with their army of Aussie and Kiwi raised second generation players are going to be a big threat for England's 3rd spot in the very short term. PNG, will get there when their young players get access to better player development programs and overseas clubs. Physically, they aren't up there with the polynesians but on interest alone, I can't see anything but improvement for PNG.
And before someones mentions PNG being a super poor third world country, may I point out that the relative GDPs will no doubt change over 50-100 years. After the 2nd world war, Australia and Argentina had similar GDPs but now Australia's is 4 times (?) larger. As long as this mining boom continues PNG is looking good to make some solid economic progress in the coming years which shouold tranlsate into a stronger Rl team.
Fan base isn't really a good indication of a teams power, nor does it provide any future indication on a teams potential. I think all the NRL clubs with massive fanbases and long premiership draughts are proof of that.
I'm not overly concerned with PNG being a 'poor' country, but more the fact that the ARL do nothing to facilitate international growth of rugby league.
Consider Origin, where you have great talents in Folau, Hayne, Uate, Tonga(lol maybe?) and other polynesian blokes who give up representing their own country in hopes of achieving in Origin, Uate recently gave up playing for Fiji just so he could get a look into NSW. In a way Origin alone is isolating talent within Australia and I won't be surprised to see a PNG team within the next 50+years made up of origin rejects/reserve graders because it's a representative alternative for most players.
PNG does have talented players, but what's the point if all of them are going to end up going to Australia, changing their allegiance to Australia and representing Australia for the sake of their career? If that keeps happening they'll never be strong. I don't see rugby league as a code that will ever develop a team or a solid, strong and consistent competition within any of the island nations.
Australians in general are narrow minded, arrogant f**kwits anyway.