WandaVision episode 8 secretly undid one of the most key parts of Thanos’ Avengers: Endgame plan by showing that the destruction of the Mind Stone never really mattered. By showing that Scarlet Witch’s powers could effectively make her a stand-in for the Stone, the Mad Titan’s removal of the Infinity Stones from the timeline wasn’t quite as definitive as he believed.
The penultimate episode of WandaVision finally explained how the MCU’s newly-named Scarlet Witch brought Vision back from the dead. In a surprising twist, it also revealed how Director Hayward’s secret S.W.O.R.D. Project Cataract revived the original Vision, turning him into the mysterious new White Vision in the post-credits scene. In both cases, Wanda’s magic was key, though in the case of Hayward’s creation of White Vision, the rules were somewhat more complex. Rather than his manifestation being part of Wanda’s Hex, her residual magic was attached to a S.W.O.R.D. drone, allowing the Cataract team to almost accidentally kick-start Vision’s corpse.
By expanding the logic of Wanda’s powers to effectively make her the Mind Stone, which follows the logic that she replaces it as the power img (after it created her), WandaVision has established that the Stone itself no longer matters. In effect, if Wanda’s experience with the Stone transformed her permanently to the point that she became not just a vessel for the Stone’s powers but a conduit for them, then others could follow suit. In other words, Thanos’ desire to destroy the Stones so that nobody else could use or abuse them is now at least partly redundant.
Wanda is, of course, far from the only MCU character to have been transformed by the Infinity Stones, or at least to have been directly impacted by their powers. Captain Marvel was empowered by the Tesseract and Red Skull was transformed by it, while Jane Foster became a vessel for the Reality Stone, the Guardians of the Galaxy all used the powers of the Power Stone, and Doctor Strange propelled himself through the multiverse using the Time Stone. In every case, the Stones may have left something behind, and combining the energy signatures would be akin to combining the Stones once more. Even without having to navigate several timelines, someone looking to weaponize the powers again together could potentially isolate them. And even if that’s only logically established by the Mind and Space Stones interactions with known characters, a single Infinity Stone has potentially devastating powers.
The question of why Thanos would overlook such a consideration actually fits with his knowledge and experience of the stones. For a megalomaniac, the Infinity Stones were an extension of powers and status – a realization of his destiny – and the history of them before his time wouldn’t matter. He also didn’t have a great deal of experience of the Stones directly, despite owning the Mind Stone at one point, so the oversight works. It’s just a strange revelation to see how the loophole of Endgame’s time heist – that they had to be returned to their own timeline – has been blown open by WandaVision and the MCU now has a possible replacement for the Infinity Stones.