So, as most people know, "400 days" features the stories of 5 different survivors, each with you making a major decision. This decision will play a factor in whether or not that survivor goes with Tavia in the Epilogue.
For a while I was questioning 400 days playing into S2. It would be hard to make a ton of dialogue for the survivors based on your choices, but we have already seen Roman's corpse and Gil's pitstop. And then, we have Eddie in the Amid the Ruins selection. Apparently this episode will have multiple backgrounds, so maybe 400 days will correlate.