I hope if they do reintroduce the SJ as a real organism, that it's part of David's narrative- not separate. I don't want to see them running around punching Humans, Androids or Xenomorphs in the chest with a big elephant trunk, it has the potential to go so stupid, so fast if they go in completely the opposite direction from Prometheus. Say what you will about the Engineers, but at least they weren't the comics' rendition of the Space Jockey.