On Asuka, I kinda of agree with everyone. So, it's a little bit hard to explain my ideas.
Basically, I think you're partially right. It would actually be cool to have a character break up from "Shinji's shadow", especially her. In the original series, Soryu's story was connected
to Shinji's. But, it was not all about him. She had her own internal struggles, her on drama. Now, in NTE, Shikinami's pure existence as a character is fundamentally connected to Shinji. I mean, she has her problems, but most of it goes right back to him. 3.0, in specific, made a lot of efforts to show how she was personally pissed with him, but still cared about his life, nevertheless (as indicated not only by the ending, but also the fact that she actually wanted his help).
Therefore, for the writers to close Shikinami's story, they have to include Shinji on the mix. It doesn't really matter if she has romantic
feelings for him, actually. What's important is that she feels
something and that must be explored. As I said before, I wouldn't mind if they ended up together. I mean, it wouldn't bother me. But that doesn't mean that I would go out of my way to make it happen. I just want Asuka to have more screen time. That's all.
On a side note, if she still "likes" him, it would be nice to see her dealing with it in a more mature manner, rather than the "tsundere thing" you've just described. If she can't handle it, I get it. But, at least, make her try.
Regarding the situation of incest, it is a very delicate topic. Personally, I think that Rei and Shinji are quite weird together. Firstly, I would never "bang" my own mother, not even if she was a clone or something. I mean, she would have different experiences and all, but that's still the body and genes of my mom. So, no. It doesn't matter that she has blue hair hahaha.
Besides that, Ayanami has always been a mother figure for Shinji, not a girlfriend. In the manga, Shinji himself reflects on it (after Asuka questioned him about it).
I never thought about this...but I don't see Shinji's voice ever changing lol. Kinda like my boy Goku.
I think that Ogata could play Shinji as an adult. She would just have to thicken her voice (kinda like what Nozawa does, but less "uplifting"). If that's not enough, which I highly doubt, just throw in Gendo's voice in the mix. They are already very similar overall hahaha
Just sit here and waste your precious time. When you want to do something, don't do it right away. Don't do it when you can. Read my posts instead. It's the only way to live a life without regrets.