The two canceled sequels for Terminator: Genisys would have dived into the origins of Skynet. After Terminator: Salvation disappointed fans and critics in 2009, the series tried to bounce back with Terminator: Genisys in 2015. Genisys brought back Arnold Schwarzenegger as a main character while also boasting an impressive cast with the likes of Emilia Clarke, Jai Courtney, and Jason Clarke. Despite Skydance's best efforts, the fifth Terminator movie didn't do as well as they had hoped.
Terminator: Genisys was supposed to be the first film in a new Terminator trilogy, but after the film performed poorly at the box office and received scathing reviews, the two sequels, as well as the planned TV show were scrapped. The sequel would have introduced another alternate timeline while explaining the origins of Matt Smith's T-5000 character. The Terminator: Genisys sequel would have also delved into the backstory of the cyborg John Connor, detailing the events that took place after Skynet took him. Now it has been revealed that fans would have gotten an even closer look at the origin of the evil artificial intelligence system.
While talking with The Production Meeting Podcast, producer and writer Patrick Lussier briefly spoke about his work on Terminator: Genisys and what the sequels could have looked like. Lussier explained that while Genisys was more of a love-letter to Terminator 2: Judgement Day, the sequels would have introduced new characters and been "trippier." He also mentioned that the film would have explained where Skynet and Smith's character came from.
Lussier clearly had a plan for the sequels, with the writer also explaining that he had written two drafts for the first sequel and outlined the third film. In the end though, the critical response of the film made Skydance scrap Lussier's plans and go in a different direction for the sixth Terminator movie, Terminator: Dark Fate. Unfortunatly for Paramount and Skydance, those plans didn't work out either, with Dark Fate being an even bigger box office bomb than Genisys. While Terminator: Dark Fate got mixed to positive reviews, many fans still wonder what the full Terminator: Genisys trilogy could have done for the franchise.
Fans saw the rise of Skynet in T2 and Terminator: Rise of the Machines, but things likely would have been very different in a Terminator: Genisys sequel since it took place in a fractured timeline. Smith's character represented the first time Skynet took a physical form, so it could have been interesting to see how that happened and what the character is fully capable of. However, Terminator: Dark Fate ditched the idea of Skynet altogether in favor of a new AI threat called Legion. Lussier's Terminator trilogy likely won't ever see the light of day, and now the fate of the entire Terminator franchise is also uncertain thanks to the latest addition to the franchise.
Source: The Production Meeting Podcast