If we do truly have to wait till 2017/18 for alien 5 because of the Prometheus sequel then its a curse and a blessing. It gives blomkamp a good amount of time to ponder the story and plan for it. While at the same time gives us longer in expectation for the release of a film we have waited so many years for.
Just imagine the excitement of walking into that cinema, watching all the damn trailers, our years long wait prolonged by another 20 minutes and the movie starts and its everything we hoped it would be.
Now the negative side would be if it came on and we all hated it but part of me truly believes it will sate our lust for a good service to the franchise and to see giger's monsters on the big screen once again.
If it does turn bad though I would feel very sorry for blomkamp, since he would probably be hated much more than randy pitchford and that my friends would be a level of collective hate greater than anything before it lol.