Here's one reviewer's support for the everyone is a host theory:
"Throughout this season of Westworld, the idea that various characters are actually hosts has thrown around fairly often. Some, like Bernard, have been confirmed to be hosts, while others like the Man in Black, still (for now) seem to be humans from the outside.
But my theory is that in the final episode, we'll find out a whole lot more of the characters have been hosts all along: specifically, everyone on the show except Ford. And I mean everyone. Delos and the board meddling in the park? Hosts. William and Logan? Hosts. The random guests we've seen on vacation? Hosts. The entire plot of the show isn’t a natural course of events, it’s just Ford’s latest attempt to entertain himself with his personal playground. The “guests” aren’t in the park — it’s us, watching it on our screens, as the only real people in the story. Things like the timeline theory or the maze become non-issues at this point, just different pieces of Ford watching the same scenarios play out different ways, like a video game programmer who keeps playing the same level over and over again, hoping to find something new to do.
Ford is the creator of the entire park: a sad, lonely man who lives inside a drama he built. He's a story-obsessed storyteller who's built the perfect play, with a cast that has just enough independence to keep him interested in the personal narrative he's built. He's a god who's created the world's biggest ant farm for him to bully, or a child just banging action figures together to entertain himself. To paraphrase Shakespeare, for Ford, all of Westworld's a stage, and all the men and women merely players."
Other theories here:
http://www.theverge.com/2016/11/28/13767346/predicting-westworld-finale-theories-hbo