Surprisingly, the Ultron one is next:
I thought that Ultron would be saved for the finale, and we'd get the Gamora-as-Thanos episode (or whatever that one's supposed to be about) for episode 8.
I wonder what's going to cause it to diverge. (it seems pretty clear that Ultron gets his consciousness put into the Vision's body, but I figure there's going to be a specific event that leads to that happening when it didn't in Age of Ultron) Part of me is expecting that Hank Pym is going to be brought in to help with the Ultron project, both to reference his role in Ultron's origins in the comics, and to make it so Hank is 3-for-3 in terms of his appearances in What-If leading to disastrous alternate realities.