It's relevant if it's more successful than retreading all the expected alien 'franchise' themes. It's opened up possibilities and as Ridley Scott has said, the Engineers are a good start, meaning there's more to be expanded on. If ancient astronauts is a jaded theme, then an 'Aliens 2' as some seem to desire wouldn't have done anything new either. As far as I'm concerned if Scott is a fan of one of the best sci fi scripts ever (Quatermass and the Pit) why shouldn't he try his own take on across a multi film epic?
Ancient astronauts, artificial humans, gods and myths, blind faith; all make for a more compelling story than 'ooh big bad Queen Xeno vs Ripley substitute.