While not officially shown or outright stated or anything, the connection is nevertheless there, just hidden. Kyurem has two signature moves not used in B/W that relate to Reshiram/Zekrom,
Freeze Bolt and
Cold Flare. Again, while not used and not outright references, They seem to possibly draw relations to Zekrom/Reshiram. Although that's still just speculation...
Also of note is that before Platinum was revealed, Giratina had no connection to Dialga/Palkia. It was found much later in the game, in a completely different spot, has many differences, from highest base stat, the specifics of its signature move (Ghost type, not Dragon, and physical not special), and appearance and info (the Pokedex states that it's from a different world. That's it). It's only link is that it was a dragon and had a signature move. It didn't even have the weak connection of unused moves possibly related to the other two that Kyurem has.
But anyways everything is just speculation at this point, really :/. The fact that there are unused moves in the game points to possible changes for Kyurem in a third release, although it could just be a special event download, which would also account for the God Stone key item. Perhaps at this point there isn't a third game coming, but GF may change their mind, or may release R/S remakes first and are focusing on them.