Jon Spaihts may have the bad luck to be a guy whose best work never gets produced. His scifi script Passengers is incredible, and everything I've heard says that his original work on the movie that became Prometheus was great as well. Certainly better than the finished film.
Spaigts' script may never see the legal light of day, but he spoke with Empire about the ways his drafts (five of them) were different from what Damon Lindelof did. The big change, of course, is that his scripts involved the original Xenomorph, and had facehuggers and chestbursters. Apparently the push to make Prometheus more original and less of a direct Alien prequel came from the Fox brass, an interesting case of studio heads having seemingly smart ideas. I mean, when we all heard this film would be not quite a prequel we got excited - it's rare that we get original scifi anymore, and a not-really prequel to Alien is the best we can hope for.
It didn't turn out so hot, of course. But what would it have been like if left to Spaihts? Apparently one of the film's best moments came from his script: the Medapod abortion scene. But his take was different.
One of the things I realised was that we hadn't seen anyone survive a classic Alien chest bursting. And I was really intrigued by the notion that a character might be infected by the parasite and know that it was coming, know they had a timeframe of a few hours, and that we would have set up previously a nearly omnipotent medical device, designed to extend life for explorers in foreign places. Our heroine would have a short time to get to the machine and extract the thing inside her. It was a very gory sequence and it plays out very much like the sequence in the film. The main difference is in choreography. At the end of the sequence as I first conceived it, the heroine manages to get the creature extracted from her and it is expelled from the pod and she's sealed inside, whereas in the final film it goes the other way.
Then she lapses in and out of consciousness for a number of hours as the machine puts her back together. As she comes back to consciousness, she sees the thing growing in the cabin outside and even killing people. So by the time she emerges from the pod eight hours later, the thing is abroad in the ship and big enough to be a huge danger. That was the original conception of the medpod scene.
How would she have been infected? David would have done it to her on purpose, but in a really interesting way. In Spaihts' draft David hates his human creators, and he thinks the Engineers are more his equal. He keeps delaying the mission so that he can attempt to make contact with the Engineers, and along the way he discovers a massive cache of alien eggs.
So at one point Shaw goes to stop him and David ties her up and deliberately exposes her to a facehugger. He caresses an egg open and out comes a facehugger. David doesn't smell like a person - his breath isn't moist - so he can handle the thing like a kitten. It doesn't want him; it's not interested. But then he exposes it to her and it goes for her like a shot. He toys with her for a bit and then lets it take her. That, in my draft, was how Shaw was implanted with the parasite that she had to remove with the medpod sequence.
How does Shaw know what happens when you're impregnated with the alien? She had horrific first hand knowledge. The scene Spaihts describes is so good, so stunning, that it being left out of the film feels like a travesty.
David, as he began to get fascinated by the science of the Engineers, doesn't deliberately contaminate Holloway with a drop of black liquid. Instead, Holloway hubristically removes his helmet in the chamber, is knocked unconscious, facehugged and wakes up not knowing what had been done to him, and stumbles back into the ship. In my draft, he returns to his cabin, is embraced by Shaw, who is delighted to see him having feared that he had died, and the two of them make love. And it's while they're making love that he bursts and dies. So that lovemaking sequence echoed my original lovemaking sequence where he explodes! It was messy.
Dammit! That's awesome!
Head to Empire to read more, including Spaihts' thoughts on what he wanted to do with future films, and how the finished film's ending compares to his ending.