When Ford originally creates the Wyatt storyline (specifically in the scene where he gives Teddy the Wyatt backstory), Ford mentions that the narrative is rested in truth. We saw this episode that the massacre that Teddy remembers as Wyatt having committed was actually committed by Dolores. This leads to several conclusions, all of which support the tinfoils across this thread.
1) There are 3 timelines (Present, 30 years ago, 35 years ago) I think it's fairly obvious at this point that we have had three timelines displayed to us. The first timeline, taking place 35 years ago, is shown to us in the Dolores flashback this episode. The hosts are basic, and some hosts (like Maeve and Armistice) are only just being introduced to the fold are are going through basic programming. At a very minimum, this establishes an initial timeline, as directly pointed out by Dolores ("when are we?"), and as proven by the buried/open church distinction. Also, Teddy's flashbacks to the "Wyatt massacre" closely if not perfectly mirror Dolores flashback, but that'll be important later. In order to establish the third timeline, we need to prove that...
2) William = MiB This has been popular since the beginning, and I think it's spelled out for the viewers at this point that William and the Man in Black are one and the same, establishing a distinction between the present and 30 years ago. There's thematic evidence behind it, such as the mirroring of William and the MiB in their picking up of Dolores's can, thinking of the park as a story that they have to finish, and the park revealing their true selves.
There is also direct evidence. MiB is a titan of industry that essentially owns the park, and William is about to marry the heiress of a company looking to invest in the park. William is about to marry when he leaves WW, and MiB was married 30 years ago (the same amount of time ago when he says he was "essentially born" in Westworld). MiB recognizes Elon Musk's ex-wife, surprised that WW had not retired her yet, and is surprised because she was the bot that welcomed him (William) upon his first visit 30 years ago. William is clearly undergoing a change in the park, and MiB's wife killed herself because he was a different man in the park than without. There is more than a preponderance of evidence here. MiB = William, establishing the 3rd timeline.
3) Dolores is Wyatt This is the big drop of this episode. As I mentioned before, Teddy's Wyatt flashback mirrors Dolores almost perfectly. We know that when hosts "relive" violent memories, they act them out (like when Maeve slashes Clemantine 2.0's throat remembering Mi, establishing that Dolores really did shoot a bunch of hosts and then put her gun to her head, as she does this in the present.
Additionally, if we take everything previous to be true, then we haven't seen Dolores in the MiB timeline for a WHILE. Like she's totally absent and we haven't noticed it because they've been feeding us past Dolores the whole time. If the storyline is actually taken from "truth," and to line up thematically with MiB's storyline AND Teddy's Wyatt storyline, it only makes sense that Dolores would be Wyatt. Wyatt has been built up to be this big boss, but it wouldn't make any sense if Wyatt was someone we haven't already met. Dolores committed the actual massacre, and is the center of the Maze that the MiB is searching for. This episode also hinted that "inside the maze," people can be killed by hosts, and Maeve's storyline shows us that the maze is a state of mind, or consciousness, or freedom or something, such that you can override your core code and hurt guests. This, if we take everything else said here to be correct, leads us to...
4) Dolores killed Arnold During the massacre, Dolores killed Arnold. Arnold's death occurred at the same time as the massacre, and maybe the massacre even resulted from Arnold's work on Dolores. Dolores is somehow linked to Arnold more than any other host, and it may be the case that Arnold told her to kill him, or got her to kill him, to prove that she is conscious and solved the maze. Ford wouldn't say that he and Dolores are friends "at all" because she is either the host that killed his dear friend, or the creation of his arch nemesis that he can't seem to crack. Dolores is posed as the ultimate enemy here by Ford to ground in truth the way that he sees her and what she did.
Damn I love this show
*Edit
After a good night's sleep and reading some of the replies, I think that it's only reasonable to come to a 5th conclusion...
5) We've only been following 1 timeline. Yup. We've been following 1 timeline the whole time. You just didn't notice it, and neither did Dolores. After the reveries were implemented (purposefully, by Ford), we start getting these alternate timelines. But the reveries are just supposed to make the hosts remember past lives. When the hosts remember, the literally "re-live" the memories instead of just vaguely remembering them. Dolores has been following her one timeline (her "path"), but has been having flashbacks, re-living past lives. When we see Dolores in the William timeline, we often see her trip out for a few seconds. Sometimes these show past versions of herself dead, showing that she got this far in the maze before but hit a literal "dead end." Sometimes we see Dolores remember things that are obviously in the past, like the Wyatt massacre. STILL OTHER TIMES though, we see Dolores more or less doing the same thing that she's doing with William, except that William isn't there. THIS is when we see Dolores as she is, in the present. She is mirroring the path she took with William to bring her to the center of the maze (the Wyatt massacre town) in order to assume the mantle of "Wyatt" and become the villain that Ford knows she can be. She has been flashing back to William's timeline, literally retracing her steps to arrive back at the town, and it's been right under our noses the whole time. Ford intended this through the reveries, as he always intended to implement this Wyatt storyline.
And remember, there's a path for everyone, and Teddy's path always leads him back to Dolores.