So I think there's a few people that could be knocking on the door on the final scene. Tyrell would be the obvious choice. We don't really know what happened to him before the time skip, but I feel like this would be the easy choice. Another possibility that I didn't think of but I read on reddit is that it could be the police. Krista's ex could've enough evidence to have him arrested, but I'd hate to see the story go in that direction. Lastly the lowest possibility is that it could be Darlene trying to figure out what the fuck he's been up to since the time skip.
Another wildcard is Joanna, ever since I was about to get the episode on Amazon I was able to read the subtitles and it doesn't translate or even show what she spoke in Danish to Elliot. There's a few redditors out there who were able to find out that she basically said "If you've harmed him at all, I will kill you. I've seen some Swedish/Danish speakers say that Tyrell is very elegant and poetic with his Swedish, and Joanna comes back with very crude and direct Danish. They've said that she shows very little empathy and it's almost like she's constantly giving him commands. Her tone doesn't exactly translate well with the subtitles.
I'm completely thrilled for the ending of Act 1. I have complete faith in the rest of the series, i'm really excited to see where else Sam Esmail is going to take Elliot.