You can't make exceptions to the rule, that's what the international body is doing now and it's a mess. My solution is you pick one country and stick to it regardless of eligability. The fringe test players will feel less inclined to bounce between countries if they know there's a good chance they won't get many international games waiting for the big guns to pick them. Giving the likes of Lebanon, the Pacific nations, USA etc a more meaningful test program will help them attract top tier players and grow the game domestically.So be it! He is South African after all as that's where he was born!
Although like I said, I do make some allowances for those who were brought to another country at a young age! But ideally, in my opinion, I beleive Merthens was born in South Africa and therefore IMO should of played for the Sproingboks!