The two timelines theory is a popular theory that continues to become more likely the more I watch. What Dave Chen (one of the hosts of the Decoding Westworld podcast) hints at in this video, but doesn't point out is in the scene in which the Man in Black (MIB for short) and Ford sit down and chat (from episode 6), MIB talks about how the park would have been closed down 30 years ago if it weren't for him, and Arnold (the co-creator) was clearly trying to destroy or set free what he had created (there have been many references to an incident that took place 30 years ago).
We know MIB to be a wealthy philanthropist (as briefly discussed in one of the earlier episodes). We also know William and Logan to be rich co-workers at some unknown company in which Logan holds power over William (in a scene that revealed their somewhat antagonistic relationship). So it's likely the show is building to a reveal of just what that incident was, and it's looking more likely that William, Logan and Dolores are somehow involved.
Don’t forget about Dolores and Bernard's frequent chats though. They often play back to back with scenes from her journey with William. It's unlikely these scenes are happening at the same time simply because it would take far too much effort to go into Westworld pull her out while William is sleeping, have a chat, and then replace her in time for William to wake up again.
That is, of course, unless each of the hosts have multiple bodies united by one mind. It would make sense from a time and resources perspective for them to keep multiple bodies of each host, and the reveal could be stunning. It could also potentially disprove some of the current crop of theories. However, it’s unlikely considering what we’ve come to know about Maeve (Thandie Newton). In fact I think it’s more likely William and Dolores eventually run into Maeve in the past software iteration she keeps seeing flashbacks to.
However, those who oppose the theory of two timelines say neither actor Ben Barnes (who plays Logan) or Jimmi Simpson (who plays William) look like Ed Harris. Though between the two, Simpson looks more like a young Ed Harris (they both have blue eyes). They also point to the fact that it would be a noticeable inconsistency in the production to digitally de-age Anthony Hopkins in order to show us a young Ford earlier in the season, but cast a different actor to play a young Man in Black (Ed Harris) simply to facilitate a plot twist. And while I can’t dispute that, I do find watching Westworld with this theory in mind infinitely more enjoyable.
If Game of Thrones has taught us anything, it’s that HBO has lots of twists up its sleeve and they like to drag them out. So even if this turns out to be true, we may not find out for some time. Nevertheless, I’ll be watching closely these next few episodes. I’m still waiting for them to reveal that someone we thought was human is actually a host, and I'm waiting with bated breath for the reveal of who Arnold was, why he did what he did, and what ultimately killed him. We'll have to wait and see.