>>27552216They would never make Sun and Moon New 3DS exclusive, there are too many people who still have an original 3DS/XL and don't want to/can't upgrade to the new one for one game. It may be New 3DS enhanced like BW/BW2 were DSi enhanced (but still ran on the DS) but they don't want to alienate that many people.
That said, I do believe the R/B New 3DS is the definitive version and I love mine. If you can get one you should.