There's a thread about Luminosity on TV Tropes, and one person had a bundle of questions that I answered there; crossposting here in case anyone's interested.
is it possible for a vampire to become fixated on a 'mate' whose orientation does not allow the attraction to be returned? Or does the mate bond override orientation?
Unspecified in canon; in Luminosity, no, everybody winds up mated to someone of approximately the correct "type" for non-magical attraction.
What about transgendered individuals who have made no modifications to the appearance they were born with — if the process takes orientation into account, then does it work on the basis of gender identity, gender presentation, anatomy, or SRY?
Again, unspecified in canon. My ruling: If you have a person A and a person B, and they are vampire mates (or one is a vampire mated to the other, a human), then A is attracted to B's whatever-mishmash-of-sex-and-gender-characteristics and vice-versa. Once the actual magical bond kicks in (i.e. once they meet), then even departures from this mold will not affect it. For instance, a vampire who is attracted to female personalities but not female bodies would have to meet a MTF transgendered mate before significant biological intervention took place, but if they met first and then interventions happened, this would not bother the vampire.
In Luminous-canon, only male werewolves can imprint on people, and (was it only Bella's hypothesis or confirmed?) this is for reasons of passing on the werewolf gene(s) — what does that mean for gay male werewolves? Werewolves born with male anatomy but who identify as (straight and) female?
I don't have a way to confirm the hypothesis in the story (exactly how would anyone verify what the imrprinting is for?), but yes, that is what it's Officially For. Imprinting can override native homosexuality (in fact, there is a character for whom this happened; I'll go into that a bit in Radiance). It would not "override" transgenderedness in any meaningful sense (wouldn't give the physically male, mentally girly wolf a different, masculine personality), but it could make her attracted to (a) woman if she weren't already. Werewolf super-healing and wonky body chemistry would make any attempts to physically transition intractable before quitting one's wolf. Quitting the wolf doesn't end the imprint, and neither would hormones/surgery/whatever; once it's there, it's there.
Or vice versa? What about infertile or asexual male werewolves? Does the imprinting go away if the werewolf becomes infertile afterwards?
Once the imprint is there, it's there. Imprinting can override native asexuality like it can override native homosexuality. A werewolf born infertile would not imprint; one that was sterilized later would keep an existing imprint if there was one but not make a new one if there wasn't.
Can a vampire feel a attraction to a mate who is in fact an inactive werewolf? If so, can that bond survive the werewolf's activation?
Unspecified in canon; I rule yes and yes, although it'd be a difficult sort of relationship.
And after a werewolf imprints on a person, can the imprinting survive that person's being turned into a vampire later on?
Yes, but it'll traumatize the wolf rather a lot.
exactly how would anyone verify what the imrprinting is for?
I don't know of how one would verify what imprinting is for, but you made a number of conclusions and rulings based on the idea that imprinting was indeed for finding the best possible mate. If one of those conclusions were wrong, that would be a piece of evidence that indicates that mating is not, perhaps, what imprinting is "Officially For."
This is Part 2 of the discussion of Alicorn's Twilight fanfic Luminosity.
LATE BREAKING EDIT: Part 3 exists now, so new comment threads should be started there rather than here.
In the vein of the Harry Potter and the Methods of Rationality discussion threads this is the place to discuss anything relating to Alicorn's Twilight fanfic Luminosity. The fanfic is also archived on Alicorn's own website.
Here is Part 1 of the discussion. Previous discussion is hidden so deeply within the first Methods of Rationality thread that it's difficult to find even if you already know it exists.
Similar to how Eliezer's fanfic popularizes material from his sequences Alicorn is using the insights from her Luminosity sequence.
The fic is really really good but there is a twist part way through that makes the fic even more worth reading than it already was, but that makes it hard to talk about because to even ask if someone is twist-aware with any specific hints is difficult. The twist is in the latter half of the story. If you are certainly not post-twist and want to save the surprise, then you should stop reading here and fall back to Part 1 discussion or to the fic itself.
If you think you're pretty sure you are post-twist and are safe to read the rest of this, try reading this rot13'ed hint and see if what you've read matches this high level description of the twist...
Rqjneq unf qvfpbirerq gur frperg gung Vfnoryyn jnf xrrcvat sebz uvz "sbe uvf bja tbbq" bhg bs srne bs Neb ernqvat Rqjneq'f zvaq. Va gur nsgrezngu, fbzrguvat unf punatrq nobhg gurve eryngvbafuvc gung znl unir pnhfrq lbh gb pel sbe n juvyr, naq juvpu znlor urycf gb rzbgvbanyyl qevir ubzr gur pbzovarq zrffntr bs YJ'f negvpyrf nobhg "fbzrguvat gb cebgrpg" naq "ernfba nf n zrzrgvp vzzhar qvfbeqre" naq gur jnl gurl pna fvzhygnarbhfyl nccyl gb crbcyr jub unir abguvat zber va gur jbeyq guna fbzr fvatyr crefba jub gurl ybir.
If the answer to the hint is obvious, then just to be sure that there is not a double illusion of transparency at work, here is the cutoff point spelled out explicitly:
Gur phgbss cbvag sbe cbfgvat urer vf gung lbh unir ernq hc gb puncgre svsgl svir (va gur snasvpgvba irefvba) be puncgre gjragl rvtug ba Nyvpbea'f jrofvgr jurer Rqjneq jnf cebonoyl vapvarengrq, Vfnoryyn fheivirf na nggrzcgrq vapvarengvba, naq fur unf gb ortha gb jbex bhg jung gb qb jvgu gur jerpxntr bs gur erfg bs ure "rgreany" yvsr.