Disney has delayed Marvel's Black Widow until 2021, a film that was originally supposed to arrive in May 2020 (and then November 2020). Due to the nature of the Marvel Cinematic Universe's interconnected story, Black Widow's multiple release delays, have had the domino effect of not only delaying every other MCU Phase 4 film but causing them to be released in a different order than originally intended (Shang-Chi will now come before Eternals). However, Phase 4 of the MCU is also introducing some Disney+ tie-in series to the Marvel movies, and Black Widow's delay may affect one series in particular: The Falcon and the Winter Soldier.
At first glance, The Falcon and the Winter Soldier doesn't look like it's reliant on Black Widow in any way. After all TFATWS takes place after the events of Avengers: Endgame and Captain America/Steve Rogers' retirement; Black Widow is set between the events of Captain America: Civil War and Avengers: Infinity War, when Natasha Romanoff (Scarlett Johansson) was on the run. They're very different eras of the MCU, separated by nearly a decade (if not a full decade, in MCU time).
However, there's still so much we don't know about the real plotline of Black Widow, or The Falcon and the Winter Soldier. And the rumors we've heard about both projects certainly leave room for some pretty big potential connections.
First, there's the obvious fact that both Black Widow and TFATWS are the only two MCU Phase 4 projects dealing in the world of espionage. Both seem to also be delving into how that shadowy world of spies and assassins and secret organizations evolves in a world where superheroes, villains, and alien beings are now a reality.
Black Widow rumors and trailer details have pointed to Natasha and her sister Yelena (Florence Pugh) trying to put a stop to some horrific new version of the Black Widow program, with some potential Super Soldier ties (embodied by David Harbour's Red Guardian).TFATWS will see Sam Wilson and Bucky Barnes taking on a new threat that requires the expertise of Helmut Zemo (Daniel Brühl). Given that Zemo had unique insights into the Soviet Super Soldier program, you can already see why MCU fans are speculating that events of Black Widow will start a chain of events in the Soviet corners of the MCU that ultimately come to fruition in The Falcon and the Winter Soldier. The Red Threat is once again a timely one, and figures like TFATWS' John Walker/US Agent could be powerful socio-political metaphors...
The other big connection fans have been noting is that both Black Widow and The Falcon and the Winter Soldier could be lead-ins to one of Phase 4's big storylines: the introduction of Marvel's Thunderbolts. That team is made of villains who masquerade as heroes - and/or villains the government recruits for espionage missions. Black Widow's Yelena and TFATWS' John Walker would easily be two great recruits for the Thunderbolts' knock-off versions of Captain America and Black Widow - not to mention Taskmaster or Zemo (one of the team's main leaders in the comics).
All of this is speculation, of course, but the ties between Black Widow and The Falcon and the Winter Soldier seem pretty clear: one has to come before the other, for the larger story to make sense. Now that Black Widow isn't arriving until May of 2021, it wouldn't be surprising if TFATWS doesn't arrive until a year after its original release date, in summer 2021.
That release window also makes sense on a production timeline. TFATWS had to stall production for most of 2020, thanks to coronavirus pandemic lockdowns and is only now rolling cameras again. This massive production needs ample time to finish shooting, do all the necessary post-production effects work, and maybe even re-shoot some big action scenes or two if things got muddled during the pandemic. Why rush it out? WandaVision will get the Marvel Disney+ train rolling in 2020, building out a big, separate, part of the Phase 4 story. There's even a chance the already-in-production Loki series could finish shooting and air before TFATWS.
The Marvel Cinematic Universe continues with WandaVision in December of 2020, and then Black Widow on May 4, 2021.