Here's MY
theory.
Kyurem is the absolute absence of both Yin and Yang, known as Wuji. In the third game, you're able to catch both Reshiram AND Zekrom, creating a void. Your options: Release them both, or defeat/catch Kyurem. We all know what choice will be forced upon you due to the game's script.
This may end up being shifted to post-national dex, since something of this magnitude will undoubtedly make it too easy to sweep the champion (or the Kyurem event itself stalls until post-nat. dex.)
It is very possible that Victini could be involved in this, and possibly tie Arceus into it (I know I'm sick of it too.) Since Arceus is 'God' that may have something to do with this 'God Stone', I have no idea if that's something one of you made up, or it really is in the game. Probably will be called "Alpha Stone" in english...
That would explain why Victini is at the beginning of the Unova dex, since Victini seeks the assistance of the most powerful one to play a hand in fixing things.
Kyurem WILL have at least one more forme... one that doesn't look so decrepit. Or, just maybe, it will be like the movie Darkrai that knew Palkia and Dialga's signature moves for some random reason, only this time it's Kyurem's corruption of such moves.
Arceus arrives, yells "HEY! Knock it off! You're buggin' the world.", zooms off, turns out Pikachu dies, then there's a big teary scene, followed by Pikachu coming back to life and everyone's happy again (that last bit was a movie only part...)
Pretty much, Nintendo will think that it sold before, so it'll sell again. I'd buy it.