Well there is so much potential for a sequel and we just wont know where they would be going.
In Alien it would appear that Android Ash did know something about that system and what they may find. The Question would be How?
Yes Prometheus mission had failed, as far as be successful and return home, but we dont know if they had transmitted some information back to Earth, we know Shaw left a Message that there is nothing but Death on LV 223 and warn not to come there, over time could that message be picked up by another Human Vessel or Mission. And yes maybe Weyland Corp or Yutani may want to find out what happened to Prometheus.
The Problem with this is that we have already seen the Temple and the Black Goo in the Urns, we know roughly what the purpose of both was or indeed what it could be used for. Do we need a mission via more Humans to find out more answers?
And yes they would come into contact with the Deacon but then we would really get a movie thats like a cross between Prometheus and Aliens.
I think we could see some aspects of the above, but just not in Prometheus 2. I think Prometheus 2 will center around what Shaw and David find on their way or when they reach the Homeworld.
The problem is not how does David and Shaw fly the ship, because well he said he knows of more ships and how to fly them and we see the ship take off.
I think that its no accident why the Elder Engineers was left out of Prometheus, the starting Sacrificial Scene seemed missing something, what was that saucer etc. Well with the Art Book we had the story board that showed a longer scene and then the actual leaked images showed it was shot.
Like how the more Alien looking Fifield Props, CGI and designs was not used for what Fifield mutated into, which i think was to save the Alien DNA for the Money Shot Engineer Face Hugged then Deacon Chest Buster Scene.
I like wise think they left the Elder Engineers out because they wanted to retain some Mystery around them and that the idea is to visit and show them in any potential sequel.
This does not mean Prometheus 2 has to have a small cast list, because some actors could play Engineers but also lets not forget if they had created Mankind who share a lot with the Engineers, how do we know that Earth was not the only planet they seeded Humans on, or indeed Humanoid looking Organism.
Look at Star Trek, the Klingons, Cardassians and Romulans are all Humanoid Races. And although not Human we can recognise the actors who play these races such as Christopher-Lloyd.
[img]http://cdn.uproxx.com/wp-content/uploads/2011/10/Christopher-Lloyd.jpg[/img]
So just because maybe Shaw is the only Human in Prometheus 2 and David the Android does not mean that Ridley can cast other Actors to play not only Engineers but other Humanoid creations.
R.I.P Sox 01/01/2006 - 11/10/2017