Alright I didn't wanna do this, but I guess I gotta lay down my explanation on why the "Trevorcard" theory really doesn't add up once you think about it, here I go:
Now we all know that Gabriel is now a vampire right? With that comes all the disadvantages of being a vampire such as weakness to sunlight, weakness to holy weapons and not being able to cast a reflection. Now let's go to know about Trevor so far, we know he's %100 human, born before the events of Lords of Shadow and he's 26 years of age and he's been trained to fight Dracula when the time comes. So far what we know from Simon's story is that Trevor never comes back from Dracula's castle, possibly presumed dead. The trailers indicate that Trevor possibly became a servant of Dracula and became a vampire too, Simon most likely knocks some sense int him and brought him back to the good side as the half vampire prince Alucard.
But wait a minute, How can a full blooded human become a half human half vampire hybrid?
Now remember when I said that vampires can't cast reflections? Well that the only thing that kinda messes with the "Trevorcard" theory. If Trevor became a vampire like Gabriel, how is it possible for him to cast a reflection on the sword but Gabriel couldn't? And if Trevor did become a vampire, he would look like the vampire grunts from Lords 1 than a elegant looking dhampir. Also, now that we got a good look at both Alucard and Trevor thanks to Gameinformer, their facial builds don't match up either. Trevor appears to look like a grown man (obvioulsy he's 26 ) but Alucard appears to look like he's still a teenager with boyish looks. We know that vampirism either slows the aging process of flat out stop it, I don't think it reverses it.
To be continued, I gotta go to sleep.