Acording to this page Scott already said no to an Extended Cut This Sucks!

[departedhero20]

http://www.ropeofsilicon.com/what-is-going-on-in-prometheus-a-universe-of-questions-answers-and-theories/

Interestingly enough, it sounds like Scott filmed more of the opening sequence than we see in the final film. Darwin Shaw, who plays one of the Engineers seen later in Prometheus, commented on Twitter saying, "You'll have to wait for the Directors cut for the full opening scene!"

Scott cut Prometheus down from two hours and 27 minutes to two hours and four minutes, which does mean there may be upwards of 23 minutes of deleted scenes. He has already said there won't be an extended cut, but extended scenes will be made available on the Blu-ray.

[LIG]

To be expected, why would you release the director's cut 1st when you can release the theatrical cut 3 times with different extra's?

I'm going to be sad and re-edit the deleted scenes back in when the DVD comes out

[The Son of Paragus]

That indeed sucks Then i hope someone can edit a cool HD fan edit like White Star edition of Cameron's Titanic which is 3.47 hours long instead of 3.15 hours.

I hoped (still hope) for an extended cut, he seemed happy to show off the extended alien cut (though that was minimal)

[MrSpaceJockey]

Darwin Shaw has to be one of the most ironic names associated with the  Prometheus film.

[Zenzucht]

To be honest, when I sat in the cinema and watched opening shots of the national park where is Dettifoss situated and Dettifoss itself.. My only thoughts were "f**k yeah"

I would love to see more of it

[Mr. Clemens]

I hoped (still hope) for an extended cut, he seemed happy to show off the extended alien cut (though that was minimal)

For the record, the director's cut of Alien is actually shorter than the theatrical cut, and is not Scott's preferred version of the film.

[The Son of Paragus]

Ah sorry, i thought it was, haven't seen the original in a while, i thought i remembered him saying in an interview he was rather pleased in showing the DC

[Mr. Clemens]

He flip-flopped on that in the press, but if you have the old Quadrilogy, there's a great note from Scott in the pamphlet where he breaks down his feelings about it.