Disney has moved its The Falcon and the Winter Soldier, is due to arrive in the fall of 2020.
Except, now, it appears it may be arriving sooner. In a video announcing what's coming to Disney+ in 2020, the Mouse House announced WandaVision will also Teyonah Parris as a grown-up Monica Rambeau (who was previously introduced to the MCU as a kid in Captain Marvel) and Elizabeth Olsen back as Wanda Maximoff, among other things. And while that means WandaVision will easily be finished in time to begin streaming this year, it's not the only reason for the release date change.
Prior to today, Disney+ had limited original content planned for 2020. Other than The Falcon and the Winter Soldier and the The Mandalorian season two this fall.
Beyond that, 2021 is still jam-packed with Marvel Studios projects, even after WandaVision's departure. Case in point: there are currently no less than tie into the story for Multiverse of Madness. Fortunately, in the wake of WandaVision's move, that should be more doable now.
Likewise, there's an opening in Marvel's 2020 slate that WandaVision ought to fill nicely. With Eternals not arriving until November, there's a large gap between those films that The Falcon and the Winter Soldier would've only been able to partly fill by arriving in the fall. Thanks to WandaVision, Marvel now has enough Disney+ series to release one in the summer and the other in the second half of 2019, spacing them out between the first two Phase 4 movies. If anything, with the benefit of hindsight, it's kind of surprising they didn't schedule Scarlet Witch and Vision's show for this year in the first place.