I really like that Idea. I know that Peter is considered Unique in the sense that there is only one of him etc.
Many have speculated that Walter still went to get RedPeter after BluePeter died (otherwise why would both universes still be falling apart). Except what happened differently was that September didn't pull them out of the water, and RedPeter drowned.
But what if everything went Exactly as it did Before. Except September did something else to Ensure that Peter's Mother didn't walk into that lab and see RedPeter alive (that's when Walter said he realized he couldn't return Peter, because of the mother's attachment).
So then Walter did end up returning Peter to the Redverse as he intended to do (in terms of Walter's slogan, "I can't lose him, Again"
Even if he Saved RedPeter from dying and didn't have to watch him Die Twice; sending him back would be losing him again.
While I like the Idea that there is only 1 Peter Bishop. I definitely think it would be a Cool Notion if RedPeter was Alive and Well as an adult living in the Redverse. And from what the first 2 Episodes of Season 4 have Shown and Not Shown us, I would say that it's Very Plausible.
So when the Peter we have come to know returns, The Imbalance caused by having 2 Alternates that are Actually Both RedPeter would probably be... Bad. And maybe we will see Peter duke it out with himself. Or, maybe we will see him sit down and have a constructive conversation. Divide up their belongings between one another, decide who will live in which universe. And of course, Try to come to an agreement over who will get Olivia while the other gets Bolivia (they could flip a silver half dollar or something). And then Eventually use The 2 Machines at the Same Time to do something super crazy.
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Arg, I thought the Idea of 2 Peters in 2 Machines at the same time was a cool springboard. But as I just remembered, The 2 Machines merged into 1 when the Bridge Room was created.
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