Luminosity/WMG

The Elspeth who doesn't sign much and the one who does represent Elspeth's power.
All she signs in chapter 12 is "it's true" in response to a true statement. This is basically what Elspeth's power is, plus a little communication--which is the Elspeth who signs.

The Volturi were significantly weakened by
She forced them to accept A lot of vampires should be really unhappy about finding out how they were being manipulated.
 * Guess at slightly more specific: Those vampires are not particularly angry at how she was keeping them together. This will turn them against Chelsea, which will slowly drive her insane, and then breaking up the Volturi when she needs to be put down--unless Aro can get Addy back. Oh my goodness.

"Singers" are all powerful witches...
And this is a survival instinct. Bella and Edward, for instance: Bella smelled good to everyone, because she blocked out all powers, but especially to Edward, because her power was most intrinsically geared to blocking his. She keeps her mind private, he makes others minds public. Pera was Bella's singer because she could get past Bella's defenses--both in hiding people/things from her, and hiding Bella. No one has noticed this pattern because powerful singers tend to end up dead. This could also mesh well with the mate bond being with powerful witches: if a witch can help you and you leave him/her human, you run a risk of running into his/her "listener". Giving a reason to turn them and guaranteeing alliance works well. Edward was a rare confluence of the two.
 * By extension, Nathan would have been Siobhan's singer. And/or possibly vice-versa.
 * This would Justify the mate bond.

Addy will find Bella
She has borrowed Siohban's power and Bella will probably be very useful.
 * Further: At least as far as Addy/the audience knows, Bella cannot give her power to Addy. Should she wish to keep Siobhan's power, there are currently two witches Addy can fight all-out: Siobhan and Bella.
 * Not really jossed but  that makes it less sense for her to be the one to find Bella.

Vampires (and potentially the wolves) are created by a powerfull Witchcraft
Vampires are more than overpowered, even if we consider the existence of creatures like both species of wolves. It is just hard to believe that they are the result of any kind of natural evolution. So they might actually be the creation of powerful witchcraft. While such level of power is rare, a witch capable of reshaping life into something like a vampire isn't all that far fetch, and even makes more sense, it is possible that originally there was a natural species of vampire inferior than the current one, that was transformed by magic in what vampires are today.

Demetri got very high-fidelity memories from Elspeth
Because they concerned. So he doesn't just vaguely know what happened to her, between vampire processing speed and focusing so closely on his mate, he lived it. Yeah.

"Little sin" is a person and the child of Alice
when Alice was saying that she won't remember "little sin", she was talking about a illegitimate child that she had while human, "sin" might even be a nickname. This would beat any other relative that Elspeth could find.

Alice can now see the futures of werewolves and half-vampires.
In canon, Alice speculates that she is "limited by [her] nature"--she can read humans okay because she was one, and vampires because she is one, but had no experience of being half-vampire/werewolf, so couldn't read them. With Addy having just performed a memory-blast, if Alice was in range then she now has those experiences.
 * Though the theory remains untouched, as of chapter 37, she hasn't been blasted.

Addy is the one that gave Aro the idea to use Marcus and Edward bodyparts
Using Marcus's eye was both unnecessary and impractical before, but he could have used a piece of Edward at any time he wanted... he just never thoughed about it. But Addy did, using Siobhan power she realized that could be done and told Aro.
 * So far, Jossed.

Someone has the power to tweak/create mate bonds.
It's mentioned several times in the story how unlikely it is that so many vampires are finding their mates at the same time, given the length of vampiric life-spans and the low number of vampires. Someone whose power was never explicitly mentioned, or someone we haven't yet met, has the power to either create or direct them. Maybe it's a matter of tweaking probabilities or something, but there's something unusual about the amount of pair-bonding going on.
 * What I figured was that most of the vampires are nomads and go years without seeing another vampire. Therefore, most of them have not met each other- and during the events of the books, many are brought together. A lot of the witches would not have met each other if not for them being in the dungeon, and Razi would have probably never met Pera except for the revolution, Maggie would have never seen her mate except for the Cullens and Bella, etc. Therefore, it's not someone tweaking the bonds, it's just that the vampires are being brought together. More mates should form as they begin living in a more colonized society.

The Blast victims are Dolls
They don't remember they own identity, have the brain blasted with a ton of different memories, think they are someone else, sounds familiar?
 * Given the transhumanist tone of the story, Bella's lack of belief in a soul, and the fact that all of the bodies' previous memories are said to have been deleted, it's entirely possible that they are for all intents and purposes the people they think they are. There does, however, seem to be some kind of quantum, probabilistic phenomena at work here; not only have we seen mate bonds get formed in bizarre and serendipitous ways, but now we're seeing the blasted humans only assuming identities of those vampires who are already deceased (as opposed to living humans or vampires and dead humans). All of the vampires that have been blasted with Aro's memory cocktail have been able to do so without their personality or identities changing at all.

This Fanfiction came before Twilight
Essentially, this was actually written before Twilight, with Radiance and Luminosity (and probably 2 other books) being published. It is well written, with character developement and a believable plot. Twilight was just a poorly written fanfiction with bad spelling, shallow characters, and a crappy plot. Somehow, the laws of time were bent out of shape, making Twilight come first and turning Luminosity into the fanfic.
 * I think we have to settle for a simple Better Than Canon.

Joham's aspirations for worldwide immortality are more realistic than Bella's
Bella's starting to consider some way of eventually turning the entire human population. Considering that the world has six billion people, and is already suffering greatly from overpopulation and resource depletion, over the long term there's no practical way of granting vampiric immortality to everybody on the planet. However, finding a way to permanently weave vampiric blood into the population, by gradually breeding all humans with vampires, generation by generation, until all humans were part vampire would easily be possible, though it requires one to accept that 99% of the human population over the next couple generations isn't salvageable without the aid of better technology.
 * Despite considering turning a better option than death, Bella is only offering the choice of turning (and many wouldn't take it), and Bella isn't planning to turn everyone in to a vampire exactly for the stated reasons. While not stated, Bella is smart enough to realize that you can't save six billion people, but she can try to save as much as she can.
 * No particular reason why having six billion vampires would be any worse than having six billion humans, actually. Aside from feeding, a vampire doesn't actually consume that many resources. Plus with everyone being smarter technological growth will outpace Malthusian limitations even faster than it already is, especially since inventors won't die or grow senile, won't get sick or tired, and won't ever forget anything.

Turning is akin to a Brain Upload.
It's explicitly stated that vampires cannot become unconsious; even if their brain is scattered in several pieces, their mind and ability to think, reason, imagine, and remember remains fully intact. This is HUGELY significant. It seems to me that the most likely explanation is that vampire venom is something a great deal more sophisticated than a simple mutagenic agent. For simplicity's sake, let's call it magical nanites. Given that vampire minds remain functional even when the brain is broken into bits, it follows that a vampire's mind resides as a distributed intelligence in the venom and not in the brain. The brain still would serve a purpose as a control nexus for the body, but vampires don't use their brains to think any more than human uses their spinal cord to think. This could also explain how venom "knows" to repair its own body but is harmful to all others: the venom is physically the same, its just running different software, which makes sense given that after a vampire turns a human, the original vampire's venom is then harmful to the resulting vampire, even though the resulting vampire got their venom from the original vampire.