Avengers: Endgame was a dramatic pileup of a decade of narrative payoff that left the MCU forever altered in its wake, but it’s possible that WandaVision might have even more of a lasting impact on the saga.
Little has been revealed about the plot of the series aside from it being a bonkers send up of the clichés of dated American sitcoms that will morph into a more familiar Marvel story. The MCU movies have, for the most part, taken inspiration from the comics rather than directly adapting them, with WandaVision seeming to be a variation on House of M, in which Scarlet Witch creates a new world to bring back her lost children (it’s complicated).
WandaVision will likely follow a similar path, seeing her deal with her grief over Vision’s death by forming a pocket universe where he’s still alive, possibly inspired by the wholesome perfection of ‘50s Americana she’s seen on TV. It’s worth remembering how young Wanda is; despite Elizabeth Olsen now being in her 30s, chronologically Wanda is not long out of her teens, and as such, emotion rather than reason will play a large part in how she reacts to situations, making her actions that much more extreme.
It’s been established that Wanda is heading towards becoming the most powerful hero in the MCU. Hell, in the final melee of Endgame she went one-on-one with Thanos and would have quite literally ripped him apart had he not ordered his warship to firebomb the battlefield and his own army in the process. It’s generally accepted that reality warping is one of the most godlike of superpowers, and seeing Wanda display this ability will further inform her growing strength and see her explore the full extent of her capabilities.
With WandaVision set to inform the events of Doctor Strange in the Multiverse of Madness, its appearances reported to include Young Avengers founding members Hulkling, Speed and Wiccan (respectively, teenage variations on Hulk, Quicksilver and a hybrid of Thor and Scarlet Witch), and feature the debut of the orbital intelligence agency S.W.O.R.D. (strongly hinted at in the post-credits scene of Spider-Man: Far From Home), there’s a lot that the series will bring to the table, and as such, it’s impossible for things to remain unchanged once reality is returned to (relative) normality. Which is why it might just end up being more important and impactful for the MCU than Endgame was.