The first casting rumor, which was for Charlize Theron, and went online April 2nd, 2011. So, a little over as year before Prometheus came out.
Now I hope people actually read the article, cause I do mention that Rik's role is completely dependant on what the final script draft recommends. The script is NOT complete yet, but Ridley Scott and Damon Lindelof, had ideas in development for Prometheus 2 well before Prometheus 1 hit theaters last June. And Ridley himself has met with Rik, according to my sources. So, there must be a role in mind, if they're already considering casting possibilities. The role in question - is apparently somehow linked to Shaw. Whether it be in a flashback scene, or her son, that I don't know. I was not able to get info on who is writing the script, at the moment, things will be very hush hush for a while. Secrecy is key with this franchise and they will be trying to hide as much as they can.
But Prometheus 2 is happening and it's progressing well behind closed doors.