Hayden Christensen is returning to Obi-Wan Kenobi TV series, but there's a potential problem with him playing Darth Vader. It's not only amazing that the Obi-Wan series is actually happening, after years and years of rumors regarding a return to the big screen, but the fact that Christensen is also coming back is even more astounding. This means that three of the main actors from the prequel era have returned to the Star Wars franchise in the Disney era.
Ian McDiarmid reprised his role as Palpatine aka Darth Sidious in Star Wars: The Rise of Skywalker. And though he wasn't a main actor in the films, Temuera Morrison also returned to Star Wars, playing Boba Fett in The Mandalorian. Soon, Ewan McGregor will be reprising his role as Obi-Wan in the Disney+ series with Christensen as Vader, and Lucasfilm is promising an epic rematch between the two, which could very well break the continuity with A New Hope's story. But that's not the only problem facing Christensen as Vader.
Since Christensen is confirmed to be playing Darth Vader in the Obi-Wan Kenobi series, that means his face may never be shown. It's possible Vader could be temporarily seen without his helmet, or there could be flashbacks showing Anakin Skywalker before he became the menacing Sith Lord, but the expectation is that he'll be in the suit the whole time. Furthermore, regardless of who was in the suit, Darth Vader is always voiced by James Earl Jones. So in reality, is bringing Christensen back even necessary? Unless someone knows it's him in the suit, there's really no point in having him return.
One of the best ways to show Clone Wars into live-action, but that's perhaps less likely.
However Lucasfilm uses Christensen as Vader, the fact that he's coming back in a major way is exciting for Star Wars fans. This is the final act of redemption for George Lucas' prequel trilogy, which has undergone a new wave of popularity over the past few years. Part of that is due to nostalgia, another part is due to opposition to Disney's Star Wars era. Regardless, though, it's all led to the possibility of giving Christensen the opportunity to don Vader's suit, and not just in one or two scenes.