The whole thing is just a little confusing to me. Apparently Reshiram and Zekrom were formed when a single pokemon split. If you look into their history it explains everything, such as yin/yang/wuji.
It definitely seemed like Kyurem was going to be that original pokemon. However, we're now seeing that Kyurem has two entirely different forms, one of which is a combination of Kyurem/Reshiram and another of Kyurem/Zekrom. At first I thought White Kyurem and Black Kyurem were fused pokemon, such as if Kyurem were a sort of parasite that took control of a host (in this case Reshiram or Zekrom depending on its form). This doesn't appear to be the case though as it seems White Kyurem and Black Kyurem are forms of Kyurem and have nothing to do with Reshiram or Zekrom other than a few similarities in appearance.
I'm also wondering if these new forms have anything to do with that original pokemon that separated to form Reshiram and Zekrom or if they're completely different from it. I hope that N still has his Reshiram/Zekrom and if you encounter the original protagonists they will also have their Reshiram/Zekrom.
Of course, we'll know the truth once the games come out but it's always fun to speculate :]