This theory requires two other things to work so keep that in mind.
1. The two timelines theory is true
2. William and Logan work for the Delos Corporation
Ok, in the first timeline William and Logan go to the park. During their stay Dolores begins to wake up as her and William travel around looking for the maze, etc. other hosts begin to show signs of wakening too. Dolores and William begin to form a relationship. The Hosts get more and more aggressive and out of control until awakened hosts, outraged at their treatment begin to attack guests and staff alike.
Dolores completely wakens and William’s suspicions are proven, Dolores is the real deal, a thinking being and not an automaton, they both fall in love as the park goes to hell around them.
Ford realizing things have gone to hell, decides to take drastic measures and initiates a full memory sweep and wipe of all hosts. “Arnold” goes off and does whatever it is he does. In the process Dolores is wiped in front of William, in essence killing her.
With Ford’s company in financial ruin facing lawsuits and funding crisis Delos steps in and buys Ford out, Ford agrees but only if he can stay in charge of Westworld and all ownership of the code in the park belongs to him. Delos agrees and the park becomes like what we see today.
Outside of the park William rises up through the ranks in Delos and attains a position of authority, even doing some good (that foundation we heard of). Meanwhile he keeps returning to the park time and time again trying to find the spark of the person that Delores was. Using his special access he arranges for longer stays and additional perks. As time passes he becomes bitter and violent, but because of changes in the park he learns of the maze and the possibility he can bring Dolores, in a sense, back to consciousness. And that is where the Man in Black’s side of the story starts.
That weird love story could be at the heart of the show and both timelines.