Phase 4 of the Marvel Cinematic Universe is building up the Young Avengers, and WandaVision nearly teased Thor's replacement in the process. Now that the original Avengers team is no longer around in the MCU, the franchise is working to establish new superheroes to protect the world. In doing so, several replacement heroes and teams have been introduced, such as Kate Bishop being the new Hawkeye and potentially leading the Young Avengers. WandaVision did its part at the start of Phase 4 to introduce two additional members of the team and could've introduced Thor's replacement in the process.
Thanks to WandaVision's story, Scarlet Witch altered the universe to create two sons, Tommy and Billy Maximoff. While they are only young kids in the show, comic book readers know that they are better known as Speed and Wiccan. Both characters are main members of the Young Avengers, but they were erased from reality by the conclusion of WandaVision, which sends Scarlet Witch in search of them. Their introductions have been followed by Kate Bishop, Eli Bradley, and Kid Loki joining the MCU, while Cassie Lang already has been introduced, too, with America Chavez on the way. The MCU has the base of its Young Avengers roster as a result, as these heroes have the powersets to "replace" Hawkeye, Captain America, Ant-Man, Quicksilver, Scarlet Witch, and Doctor Strange.
It now appears that WandaVision considered positioning Wiccan as Thor's replacement early on. Concept art featured in Marvel's The Art of WandaVision included a big keyframe from the Halloween episode, and it is in this piece that Billy Maximoff's costume differs from the final product. Instead of wearing a suit that closely resembles Wiccan's comic book costume, as he ultimately did in the show, Billy is shown wearing something that resembles Thor's classic costume look. A version of the winged helmet and a red cape are featured, which is a reference to Billy's time in the comics as the hero named Asgardian. He originally took this name to act as Thor's replacement on the Young Avengers, and it now seems WandaVision nearly did the same.
Although Wiccan's Asgardian costume would've been a fun nod to the comics, it is understandable that Marvel didn't bother using this costume. His time in the comics as "Asgardian" only lasted for five issues, as William Kaplan changed his superhero name to Wiccan in Young Avengers #6. While the MCU can still make use of his Thor-like abilities that involve lightning, Billy Maximoff has so far demonstrated magical powers more like Scarlet Witch in the MCU. The electrokinesis could come down the road, but it is quite clear that the MCU is steering Wiccan's power set directly toward magic. For that reason, it makes sense that WandaVision didn't position him as the Young Avengers' version of Thor.
Wiccan might not be Thor's Young Avenger replacement, but he'll still surely be a key piece of the team and the MCU's future. He's destined to become an incredibly powerful being known as Demiurge and he worked with the Young Avengers on countless missions. It is difficult to imagine the MCU forming the young team and not having Wiccan be part of the lineup in some form, that is assuming Scarlet Witch finds him again in Doctor Strange in the Multiverse of Madness. When that does happen, Wiccan should take his rightful place as one of the Young Avengers' most powerful members despite WandaVision moving away from his Thor connection.