Doctor Strange in the Multiverse of Madness introduces the concept of incursions, and if you're a fan of Jonathan Hickman's Marvel Comics work, you'll know what a big deal that is. Like in the MCU, incursions occur when two different realities collide, and on the page, this led to Secret Wars.
During that event, a new world was created made up of various realities (which is what eventually brought Spider-Gwen and Miles Morales into the main Marvel Universe). Needless to say, that could prove the perfect way to reboot some characters and bring others, like the X-Men, into the MCU.
Talking to io9, Doctor Strange in the Multiverse of Madness writer Michael Waldron was asked to elaborate on the introduction of incursions and whether they could be leading to something more.
"Well, I guess I think of it akin to it in the way that as soon as the MCU introduced the notion of space, of going to space, they teased Thanos almost immediately," he teased. "There was Thor. And then Avengers was the first movie where there was a threat from the stars. And here comes Thanos. Obviously, there was a big build from there. So I think that maybe I always thought of the Multiverse as kind of like, 'OK, this is space.' You know, once upon a time, the MCU left Earth and went to the stars, now we’re going into the multiverse. So yeah we’ll see what happens with these incursions."
Making it clear we haven't seen the last of them, Waldron then ominously teased, "They’re bad news."
We get a hint at what might come next when Clea makes her MCU debut and tells Stephen Strange she needs his help with an incursion his actions have caused. With that, they head into the Dark Dimension together, and we're assuming more about incursions will be revealed in Doctor Strange 3.
As for Secret Wars, the prevailing theory is that the Russo Brothers will return to direct that movie for Marvel Studios. How long we'll be waiting until it becomes a reality is a mystery for now, though.