1. Eggmorphing (may/may not be canon)
2. Dead, from starvation obviously.
3. Concept replaced by the Neomorph.
4. Using Elizabeth Shaw's ovaries lead to the Alien.
5. A bigger Big Chap, as Engineers are just bigger humans, down to the DNA- Prometheus tells us.
6. Sure, I don't see that being explored to be honest.
7. Definitely a thing.
8. Definitely a thing.
The Neomorphs, although I'd like to see them again- got fully explored, by my count you only have the practices of the Engineers which "got sidetracked" and that's something better left mostly ambiguous, unless you're going to use it to say something meaningful about the whole Creator and Created cycle that's going on.
The LV-426 Derelict will apparently be the culmination in some fashion of the Prequel storyline.