Hard R doesn't sound good to me. Gore isn't scary anymore. I mean, stuff we see on TV these days is super gory and it is safe to say that most of us have gotten used to it, which is sad.
Something that is timelessly scary is the unknown. Not knowing what happened to people is scary. Giving a hint, or showing traces of what happened is even scarier. Giving conflicting hints/traces about what happened is the scariest of them all. Also, gorging in dissonant sounds and audio, imposing suspense and haunting uncertainty will take you to places that scares you on a really disturbing level. Alien has all the potential. The movie makers just have to take a few steps back and treat and portray the Alien in a new way. We know about the chestbursting, headbiting and facehuggers already; just like the rest of you've said, that stuff really doesn't have to show up in the film - suggesting that it happened has a much bigger effect because it lets us imagining what happened, and imagining to be chestbursted, head-bitten or facehugged will always be more horrifying due to our own imagination. I really hope that the delve into new concepts and elaborate more on the Alien, making it alien and unpredictable again. Scott better show us some Egg-Morphing and he better not drop the ball on that one since it's such a horrifying concept.