I wouldn't be surprised if FOX is attempting to open this up so Alien can go on by itself in tandem with Prometheus.
At least, I hope so, because I will remind everyone again that if this isn't the case, we will no doubt end up with an ALIEN remake.
There is also a good chance we will get a remake and a sequel with the same film. IE: A Remake that can also be a sequel if you want it be.
In my fan-obsessed mind, Im hoping the Sgourney Weaver's interest has led Fox Execs to ask Ridley to re-draft PROMETHEUS 2 so that a third film can cross over with ALIEN 5 and feature Ripley's final story.
Weaver seems eager to do it, Im sure somewhere between her and Ridley during EXODUS, this has come up.