First, I think we need to be clear - i.e., here is what I think is the case - with the multiple realities we've been seeing this year. They came into being, in their current form, when the Eternal Bald Observers not only whipped Peter out of existence at the end of last season but, in doing so, also made him never having existed in the first place. And what this therefore did is significantly alter both our reality (with Walter, Olivia, etc) and the alternate reality (with Walternate, Fauxlivia, etc), so that characters who died in either of the original realities could now be alive in the new sans-Peter realities, characters we didn't know before in one of the original realities could be now be on center stage, etc. Lincoln Lee would be an example of an excellent character who now has a role in our reality as well as the alternate.
Peter - if this analysis is correct - does not quite have it right when he says he wants to go home to a third reality. Because this implies that there are three or more co-realities - Walter now with no Peter in the past (both Peters died), Walternate now with no Peter in the past (both Peters died), and the reality of the first three seasons (alternate Peter taken by Walter, and Peter lives and grows up in our reality). I would say that third reality does not exist in the same way that the first two do. The only way Peter can get back to that reality is if the Eternal Bald Observers or someone somehow reverses his being yanked out of existence and memories, or at very least Walter, Olivia (and perhaps Walternate and Fauxlivia) get back their original memories.
Ok, so, with that in mind, we had a fabulous, action-packed episode last night, with Peter and Lincoln Lee (our Lincoln) going over to the alternate reality. Peter hopes Walternate can get Peter back to the reality where the people he loves (Walter and Olivia) know and love him. Lincoln's hoping he can learn more about how Waltnernate is responsible for the new scourge of shape shifters in our reality.
They of course get neither - and we can get something much better. Peter meets his mother - his real, alternate reality mother - on the other side. She's alive in this alternate (with no memory of Peter) version of reality. Powerful, satisfying scenes. (By the way, alternate-Broyles is alive here, too.)
And as for the shape shifters? Well, Walternate's apparently not responsible for them. The man behind them is no other than David Robert Jones, he of teleporting from Germany to the US and other scientific wonders fame from Fringe long ago. He's almost in Walter's and Bell's league as far as sheer scientific brilliance and chutzpah. He played a major role in earlier Fringe, dying as he tried to cross the portal to the alternate reality and Walter closed it - slicing Jones in half in the process. But Jones had not been sliced in the new realities our characters are now inhabiting and contesting. Should be some good times ahead with Jones back in play.
And that's the not all. In a stunning last scene, an Eternal Bald Observer - September, the main one we've seen over the years - comes to see Olivia, on our side of the portal, where she's waiting for Peter and our Lincoln Lee to return. He's gasping, and tells Olivia with regret that she will die in all realities. And he's gasping because he's shot in the chest. And he disappears.
Just on the last point - he disappears because he dies? Nah. I'd say he disappears because someone did something somewhere down the line to trigger an alternate world in which this EBO never existed at all. Maybe that's part of the process Peter getting back to the people he loves.
But who shot him and in what circumstances? And surely Olivia has some option for life that even the EBO doesn't know (though, I suppose we could have a Fringe in which only Fauxlivia lives, and she and Peter get together - again). Should be good viewing indeed for the rest of this season.
... Fringe 4.2: Better and Worse Selves ... Fringe 4.3: Sanity and Son ... Fringe 4.4: Peter's Back, Ectoplasm, and McLuhan ... Fringe 4.5: Double Return ... Fringe 4.6: Time Slips ... Fringe 4.7: The Invisible Man