This is a very interesting topic. I can see it from both sides.
For me there is a huge difference between a NZ born player who has come through the junior representative ranks in Australia (like Sonny Bell) who wants to play State Of Origin at senior level and that of NZer who comes to Aussie has a couple of good seasons in the NRL and then wants to play in State Of Origin. The former, I believe yes they should be up for consideration, the later, no they shouldn't.
I think the biggest difference in this arguement is that for you Aussies this is about State Of Origin and for Kiwis this is about international football. Us Kiwis will always play second (sometimes third) fiddle to Australia in the international arena. Its only every now and then that the Kiwis pull of some great surprise and upset. One of Sonny Bell's points was that NZ lacks any top level representative games prior to any end of season test series. Australian players have up to four, if you include City v Country. State Of Origin has become the top level of representative league in the world and its only natural for any player to strive to play at the higgest level possible, the trouble is that some players who are eligable to play for NZ (like Karmichael Hunt) are forced to turn down the opportunity to play for their country of birth in order to have the opportunity to play State of Origin, I see this as really unfair. NRL clubs have a long history and association with NZ clubs in finding young talent, it makes sense to get these players young and into the Aussie system as soon as possible to develope any talent. However why should NZ be disadvantaged at international level by allowing young players to develope under Australian coachs, clubs, etc? Afterall Willie Mason, Toni Carroll & Karmichael Hunt are all NZ born players who could of played for NZ (well Carroll did - but since then he is back playing for Aussie).
I guess the answer lies in at what age is considered as their first senior game in a state. Regardless of whether a player is a NZer or Aussie then if they play that game at that age then they should be eligable for selection for that State. If its some dude who was developed in New Zealand and stepped of the plane and made his debut in the NRL as a twenty somethiing then definately the NZ player should not be eligable for selection.