Any young player that comes through the system now will put down the kangaroos as there first choice and won't commit to the their heritage because they don't want to lose their chance at Origin if they hit their peak form. If this rule came in before Bizza, Critta and Luai committed to Samoa I don't think we'll ever see those guys putting on the Samoan jersey until the end of there career knowing they won't play Origin again.
Look at RU they had the 1 nation for life rule. The island teams tried to get the island players from the nz system but none of them committed in case they make the Abs. It destroyed the island nations development. They recently changed their eligibility rule because the island teams were basically left with local talent, and every local talent that showed potential were poached at a young age to Europe or Nz and Australia, and they end up playing for those nations because of the money. Origin is the biggest block to the international game. Kiwis suffer from it because they can't get Ponga and if they change the one nation rule none of those heritage players will commit to the island nations. JT and Fifita wouldn't able to resurrect the Tongan team because they would've been stuck with the Kiwis and Kangaroos if that 1 nation rule was applied at the time
Even if 25% of eligible players for Tonga commit to them, It allows the side to build for the future.
Take Tonga. They will have a teenage halves pairing, If the rule was in place you'd expect them to be good for up to 10 years. That allows TV deals sponsorships, future tours
As it sits now, No way are you planning anything even for next year because you don't know the make up of the side.
The flow on is tests become an after thought, fans can't book travel like they can for Rugby, Soccer etc