In 411, December finds out that September didn’t get rid of the traces left of Peter in this new timeline. So, I’m assuming the mini-Observer-conference that will take place in 414 from the promo will see him declare September a rogue!Observer and order his execution. Someone (probably the Observer assassin that Peter didn’t kill in this timeline) then shoots September, but he survives and appears to Olivia in 408 to warn her about dying in all possible futures. Then he disappears from the opera house to appear in Walter’s lab in 414 again to warn him to stick with Olivia, and to hopefully be saved by the Bishop genius.
Maybe he always knew that one day his life will depend on Walter/Peter and that’s why, in at least one universe/timeline, he saved them from Reiden Lake.
Olivia: My stepfather did this. He hits me. That’s when I crossed over to the other universe. (gives him her book) Look. That’s where I saw the blimps. Just like you said. They were in the sky in the other universe. (crying) Can you make him stop hitting me? Please.
Thoughts & Theory Time
I thought I read somewhere before Season Three started when we all found out we’d get to meet Marilyn Dunham that there was some kinda connection between the Dunhams and the Bishops.
What if - after the above scene - Walternate, curious and hopeful and desperate, looked up the Olivia Dunham (and her family) of his world and scared the living shizz out of her stepfather before he could even start abusing her or her mother.
By inadvertently telling Walternate about the two different universes, our Olivia was the one who ended up setting in motion the very war from which she’s supposed to save our worlds, and creating for herself a nemesis, the other Olivia, who she thinks is better.
Landscape With The Fall Of Icarus by Pieter Bruegel (The painting is well known because it showed that when Icarus fell and drowned, apparently nobody observed the event, or cared - the ploughman kept ploughing, the shepherd kept shepherding & the fisherman was only slightly curious why he wasn’t getting a bite. But this is now part of Fringe - so, nothing is as it seems.)
“…they glanced up and saw Icarus float through the sky, and taking him for a god, they stood still in wonder.” - Walter (who totes ignored Icarus’ dad, Daedalus, in his quote; which is interesting because Walter is the dad & Pea is the I-Wanna-Touch-The-Sun-With-My-Waxy-Wings in this story, right?)