I'm about 100% convinced that William is the MiB at this point, after thinking last week there was no chance. They intentionally tried to confuse the issue, but I'm ok with that. There are just too many reasons now for it to not be him.
-We know William is in the past because his friend talked about the creator's suicide and how the park was bleeding money afterwards. There's no way it's been in a nosedive towards bankruptcy for 30 years, so their scenes are in the past.
-We get to see the transformation of William from a tentative noob to the cold-hearted player he has become.
-We also get to see the transformation of William from corporate underling to world-renowned philanthropist or whatever his exact role in society is.
-"That man gets whatever he wants." We're going to find out why, we're going to find out how he saved the park from Arnold's plot.
-It's a good bet that some share in the park was sold shortly after William's scenes in the past, either to his company or to some other, and that is where the board from the present has come from.
His brother in law was just trying to get under his skin, to unleash the beast within? When William left him while he was getting lit up by the army, dude actually gave a smile as William was walking away.
I joked a few episodes back that MiB was the hero, but really, he's going to be the hero of the story. He is the only hero we have! It's going to be epic seeing him slay General v'Ghera.