@Wishmaker Jirachi: And why, or more precisely, how do your theory stands? The Pokédex entry says it waits for a hero to fill its body, but that is not mutually exclusive to my idea of the fusion in the game being forced: when the hero comes, the dragons would fuse together willlingly, no need to be forced to. Since the dragons were originally one which split apart due to conflict between its trainer (the twin heroes), it means that as long as they're not one, such conflict remains, so probably all of them desire the conflict to end and when that happens, they'll fuse. So I actually agree with you in that it has a strong desire to fuse with Reshiram and Zekrom (and yes, you made me see that the Splicers might be Kyurem's manifestation of said desire). But that desire alone doesn't justify its methods of forcing a fusion. In the end, such strong desire is irrelevant when it comes to R&Z's will, who are the ones who decide when to fuse back. The fact that Kyurem is able to perform a fusion and force the other dragons into it, makes it somewhat of a renegade Pokémon towards R&Z, the fact that it achieves it via an object created by itself (accepting your thoery that tha Splicers are the manifestation of Kyurem's desire to fuse back) only worsens that and that is why that fusion we saw can't be considered an advance towards reuniting the Original Dragon.
The entry says it "waits" for a hero to fill its body, not that it actively searches for them, let alone actively making others fuse with it. See? the Pokédex doesn't say that Kyurem actively attempts for to be caught by the hero or fuse with the other dragons, and that's where your theory fails- it simply waits. And what we saw is not Kyurem waiting to be summoned by the hero or its dragon counterparts, it attacks them; as for the DNA Splicers, if they are a manifestation of Kyurem's will to fuse with the other dragons, it is still an artifical way of fusing with them, since, as I've said many times before, a natural fusion would be triggered by Reshiram and/or Zekrom, not by Kyurem. When the hero appears, the Dragons will fuse together again willingly and on their own, no need for any item, not even if it was 'naturally' created by Kyurem, None of these situations are the case when using the Splicers.
As for your point of "it was a forced fusion because it was controlled by Team Plasma at the time", Ghetsis doesn't order Kyurem to absorb N's dragon: Kyurem attacks it on its own account, and it is only after it's been turned back into the Light/Dark Stone that Ghetsis tells it to absorb the stone, but the fusion had already been started by Kyurem nevertheless. However, you might be right on this one, maybe under other circumstances, the dragon would have accepted to fuse without resistance and only this time it opposed to Kyurem because it knew it wasn't the right time and that Ghetsis wasn't the hero. But still, the fact that there is a fusion that can be achieved by Kyurem forcing the other dragons, makes me think that it would not be be perfect fusion (i.e. the Original Dragon). "The body is complete and Kyurem is full", you said, but I already said that being 'full' is not the only ingredient for restoring the Original Dragon (see my Majin Buu comparison above for more details about this, if you please); remember that the all is more than just the sum of its parts: cramming the parts together doesn't automatically means that it is complete, let alone perfect.
Also, the Dex says it waits for its body to be filled "with truth and ideals", which is obviously a metaphor, thus it may not necessarily mean that it wants its body to be filled in with another Pokémon, just that it is searching for enlightment, given that Reshiram and Zekrom represent truth and ideals, but Kyurem doesn't represent anything; its essence is empty and so it might be searching for someone (a hero?) to enlighten it and fill its heart.
As for your last question, the thing is that N's dragon doesn't "help" (as you said), it is merely used, which is different. Plus, It didn't sense the fusion happening, it sensed Kyurem suffering, it didn't come to the Chasm to help in the fusion, it came to liberate it from its suffering; I don't see where you 're trying to get with that question, so I'd appreciate some clarification from you in that regard.
All in all, B/W Kyurem is not "halfway to the OD" as someone else said before, but a completely new creature, that is why it is listed as a Kyurem forme, not a separate Pokémon nor a Reshiram or Zekrom forme. Had the box mascots been called instead "Gray Reshiram" and "Gray Zekrom", I would say that yes, that creature is the first step to reuniting the Dragon, but that was not the case.