Many were surprised when Neo and Trinity were announced for The Matrix 4, but their returns were actually set up well in advance. The Matrix trilogy concluded in 2003, and even though the 2 sequels were (and still are) considered vastly inferior to the 1999 original, there were repeated calls for another big screen Matrix adventure, with the legacy of the franchise only strengthening over the past 17 years. Finally, The Matrix 4 was confirmed in 2019, and although production has been temporarily halted due to the pandemic, filming is underway. Story details remain predictably sparse, but The Matrix 4 is confirmed to feature the returns of Keanu Reeves as Neo and Carrie-Anne Moss as Trinity, alongside a selection of other familiar faces and talented newcomers.
Although The Matrix 4 marks the first cinematic outing for the Wachowskis' world since 2003, the story has already been developed via other forms of media, most notably The Matrix Online. Launching in 2005, The Matrix Online was an ambitious MMORPG project that picked up in the wake of The Matrix Revolutions and carried the story onward with a series of major events. Morpheus died (which could explain Laurence Fishburne's absence from The Matrix 4's cast), the war against the Machines restarted (which could explain The Matrix 4 happening at all) and, more importantly, it was implied to varying degrees that both Neo and Trinity could still be alive.
Neo's return was a recurring theme in The Matrix Online. Morpheus' death only happened because he was angered by the Machines' refusal to return Neo's remains following the events of The Matrix Revolutions. Aside from the suspicious lack of a body, the game also introduced the idea that Neo's code still lived inside The Matrix itself, just in case The One was ever needed in the future. A mysterious message saying "Neo not dead" from someone claiming to be Morpheus and a character called "Sarah Edmontons" (Thomas Anderson anagram) added further fuel to the theory that Neo did not die at the end of the Matrix trilogy. Unfortunately, The Matrix Online was canned before this story was completed, but it certainly seemed that The One was still alive in one form or another.
While there are less clues to tease Trinity's survival, question marks surrounding her fate were definitely raised in The Matrix Online. Unlike Neo, Trinity lacks the mystical powers of The One, and her death is fairly cut-and-dry in The Matrix Revolutions. However, the exile program responsible for killing Morpheus claimed that he was prevented from processing Trinity's body after it was recovered from the wreck of the ship she and Neo flew into the Machine city. Once again, The Matrix Online never got around to explaining the meaning behind the mystery, but it's clear that a conspiracy surrounding Neo and Trinity is afoot, and someone had a posthumous purpose for both their bodies.
It's far from guaranteed that The Matrix 4 will take the events of The Matrix Online into consideration, but the game was billed as canon upon release, and more than a few dots line up with Lana Wachowski's upcoming cinematic continuation. If the 2 are somehow connected, this would suggest that Neo and Trinity are being brought back not by their friends, but by a mystery figure with a powerful influence over the Matrix. This could be the Machines themselves, seeking to band together against a greater oncoming threat, or The Merovingian, who is also slated to return in The Matrix 4. In either case, Neo and Trinity's real-world bodies are missing under suspicious circumstances, paving the way for their respective resurrections.
