I hope I'm up for it. I'm intrigued by the way you presented Elias, and I have an image burned into my mind of his asking Kristina, "Are there many of us?" That speaks volumes to me about how alone in his solitary existence Elias is at that time. I mean at around three-quarters of century, he hasn't been able to answer that question for himself.
Anyway, intrigued as I am, I still don't know if I'm up for it. Won't stop me from reading, though.
Here's the showstopper for me writing about Elias in the times before Blackeberg -- I haven't read the novel. I depend on things said on the forum to get knowledge of it, but that isn't enough. So, instead of trying to add to the wonderful pictures you have drawn of Elias, I must wait until something inspires me to write more about film Eli or post-film Eli.
I identified this problem for myself before I even wrote "When I Am with You," but I imagined it would just be a matter of time before I took on the whole LTROI universe. Hasn't happened yet, so no historical fan fic is on my horizon.
Still, here is an opportunity for me to share with you how I see Eli. Forgive the feminine pronoun, but I see Eli/Elias as androgynous, and I simply choose
she an alternative to
he or
it. In Kristina, you have her easily identifying Elias a boy by the way he moves. I believe that is completely appropriate for novel Elias.
I see Eli being able to survive for so long based on her heightened senses and strength, but mainly I see the infection itself making major survival decisions -- "Sleep now. Feed now. Flee. Hide." This means I see an Eli who is minimally crafty, just mainly reactive and with the element of surprise always on her side -- hit fast and split. Shock and awe. The way I see her also includes living in the moment, reactive with split-second action when needed, but quiet and still when not. For that reason, I don't see her making contingency plans or spending much thought about discovery. Rather than having a bolt hole -- which even a rabbit has enough sense to have -- I see her as completely confident that she will find the next safe place when circumstances dictate a move. I suppose this conflicts with the role of adult helpers in her life. I notice when speaking of Oskar and Eli on the run, fan fiction writers have to account for how two kids can navigate an urban environment. Makes sense, but they'll come up with something. And, if Oskar is turned, there's two of them infected with a cunning infection that will compel them to do the right thing. This would be a pretty boring couple of protagonists, but in Eli and Oskar's case, they have an emotional dimension that adds the necessary depth and complexity to any tale. And we have the possibility that just being together will let them discover a sense of humor and a playfulness that both lacked when they were alone. Okay, I'd better stop here. I'm right now finding that I have some of the elements of a new story, thanks to your encouragement.
We'll see. But it would necessarily be film Oskar and Eli. It's all I got!
How could I not? But when I write fan fictions for LTROI, I most often end up writing the Eli that I imagine. And my Eli is much grittier, wary, and doomed to be forever tormented by what he is. I end up not at all seeing vampirism as anything romantic. Horrible, in fact. And that's what I was drawing up on in creating the Kristina character. The young girl, teenager, in Kristina is destroyed completely by what happens to her. How she comes to be what she is, the very thing Eli says he is not **, is something I don't think I got into that far with the Kristina story as it is right now.
We can do a couple pages each night. Just enough to keep you awake for the next eight hours. 
I now see Eli in all troubled children up into their 'tweens' and sometimes, even beyond. And none of these real-world children's crimes can come close to matching the legions of innocent folks Eli has killed, no matter what the reasons. Would I not be a hypocrite if I couldn't even give them the benefit of the doubt?