There's a bit of a power vacuum in the MCU right now. The Avengers as we knew them are no more; either dead, retired, or somewhere in between. Though there's no real shortage of superpowered individuals hanging around Earth, in one way or another (there's a whole city of Asgardians out there, after all), there's no real organization. That's why poor, put-upon Peter Parker was summoned by Nick Fury and company to save the world in Spider-Man: Far From Home even though he really, really wanted to just hang out and be a teenager for once.
But the thing about vacuums is that nature abhors them, so it's really only a matter of time before they're filled in one way or another.
Thankfully, we've already been presented with some clues as to just how that particular conundrum may be solved in the future of the MCU--and it all comes down to one of Marvel's most unlikely "superhero" teams: the Thunderbolts.
The Thunderbolts are, realistically speaking, not exactly heroes. They got their start as a literal re-brand of the Masters Of Evil, a C-list super-villain team-up that occasionally caused trouble for individual Avengers but never really made much of a mark. They were able to casually make a new name for themselves because the Marvel Comics universe had the exact same problem the MCU does right now--there was no other team of heroes around to stop them.
It went down like this.
In the late '90s when comics were at their most ridiculous, an X-Men villain named Onslaught managed to vacuum up not only a huge chunk of the X-roster, but the vast majority of the Avengers and the Fantastic Four into a sort of psionic vortex, functionally killing them in the public eye. It probably would have been sad if it weren't so completely overwrought with '90s cliches--but regardless, the end result was the same: the world in a state of panic as a bunch of villains ran around totally unchecked. The heroes that were left in Onslaught's wake were too disorganized or had their bandwidths too taxed to really fill the void left by the big institutions which meant basically everything was in disarray.
Always the opportunist, Zemo--the villain from MCU's Captain America: Civil War--saw the chaos as a chance to make an unexpected play. Rather than going for the full-frontal assault like so many other supervillains were doing in Onslaught's aftermath, he realized there was more profit in trying to play into the public's fear and anxiety rather than against it. If the world wanted a new superhero team, he'd give them one. The Masters of Evil went through a total re-skin: Zemo adopted the identity Citizen V, Screaming Mimi became Songbird, Goliath became Atlas, The Fixer became Techno, Moonstone became Meteorite, and Beetle became Mach-1.
The goal was to earn public trust and favor which would allow the Masters of Evil--er, the Thunderbolts--to insinuate themselves in the top-secret, high-security areas usually reserved for the big hero teams. After all, why bother trying to break into places like Avengers Mansion or the Baxter Building if you could have someone hand you the keys instead? And imagine all the evil that could be accomplished with unlimited and unsupervised access to the world's mightiest heroes tech and databases.
Hilariously, the plan worked almost too well. The Thunderbolts debuted and were almost immediately accepted by an adoring public. It took them less than a week to tear the Fantastic Four logo off the Baxter Building and put their own on it instead. Absolutely no one questioned them. The government and local news loved them. For a few brief and wonderful moments, everything was coming up Zemo--but then something strange started happening.
The more good the Thunderbolts pretended to do to maintain the con, the less interested in real villainy some of the members became. Naturally, it all eventually fell apart when the team turned on itself--but a Thunderbolts legacy was established nonetheless. Those among them that actually did develop a taste for heroism joined forces with other more established Marvel heroes and did their best to bring about some form of redemption or another.
That's the place the Thunderbolts have more or less existed in for the past few decades. Their roster has grown, shrank, and shifted, and their goals aren't always the noblest, but the recurring themes of trying to reform and create a new life from the shadow of an old, less desirable one have become a foundational part of the Thunderbolts lifestyle. Even Zemo, one of the primary driving forces behind the major villain moments the Thunderbolts have experienced over the years, has time and time again found himself sort-of-kind-of on the side of the angels.
So where does this fit into the MCU?
With Daniel Bruhl's confirmed return as Helmut Zemo for The Falcon And The Winter Soldier, the MCU has the perfect opportunity to start and wind a brand new narrative thread into the live-action universe. It's not that Bruhl's Zemo and the Zemo of the comics are all that similar--they're not, though it seems that Bruhl will finally be donning a more comics-accurate costume for the Disney+ show, so that gap is closing--but he does share some of the same megalomaniacal delusions.
Let's not forget that MCU Zemo's entire plan during Captain America: Civil War revolved around an astonishingly convoluted scheme to frame a brainwashed super-soldier for murder and make two heroes fight each other to, hopefully, both ruin their lives and sully public opinion on them so much they could never bounce back. He may not be the most conventional bad guy the MCU has ever seen, but he's certainly one of the most creative and tenacious, which falls perfectly in line with his comic book counterpart's original Thunderbolts grift.
That said, the MCU's current status quo mirrors Marvel Comics post-Onslaught reality almost too well--albeit without all the cringe-worthy '90s tropes and dated artwork cluttering the place up. There's a real need, as we've seen, for a team to emerge--and based on the current Phase 4 announcements, there are no new teams waiting in the wings.
Add to that the fact that the MCU is currently littered with disparate plot threads and half-dealt-with villains, all of whom could be primed and ready for a major comeback, and even potentially a redemption arc, and you've got yourself a very specific recipe.
In addition to Zemo, the MCU is littered with villains and anti-heroes who are waiting in the wings for a comeback. Ant-Man & The Wasp's Ghost (and Bill "Goliath" Foster) both have more stories to tell, Dr. Strange's Mordo was teased as a villain in a stinger that has yet to pay off, Spider-Man: Homecoming's Vulture is unlikely to return, but his entire crew of blue-collar criminals was populated with plenty of characters who could be developed further. The same could be said for Far From Home's Mysterio, who was surrounded by a team of disgruntled scientists who could easily become more than just supporting roles. Then there's Bucky Barnes, who will (probably) need something to do after The Falcon & The Winter Soldier, considering he is not going to be wielding the shield and Yelena Belova, the new Black Widow being introduced in Natasha Romanov's solo movie, both of whom have Thunderbolts ties over in the comics.
Sure, the relative star power and name recognition of that roster may not be on par with say, The Avengers, but Marvel Studios has made quite the name for itself in taking otherwise B and C-list characters and turning them into mega-stars--which, really, beyond the will-they-or-won't-they redemption arcs, deception, and situational absurdity, is really what the Thunderbolts are all about.
Besides, if Spider-Man really is out of the MCU for good, then somebody is going to have to come in to pick up the slack, right?