Sadie Sink Speculation
Marvel Strike Force has a habit of putting characters into the game to tie in with movies and TV shows.
For July, they're adding both Julia Carpenter and Rachel Cole-Alves into the game and adding them to a team called the Amazing Avengers with Spider-Man and Hulk.
They've done this in the past with MCU movies, adding characters to the roster and creating their own in-game teams, paying homage to them, but not in a carbon-copy way.
Now, yes, this could be a coincidence, or this could be the devs messing with us. Sadie Sink character speculation started with Rachel Cole-Alves. The character is very niche to be adding to the game at this time when there are more popular comic characters. I think most of us ruled out Julia Carpenter, Spider-Woman/Arachne, because of Madame Web. Then I remembered they called her Julia Cornwall, which I remember thinking was odd at the time, as she is much better known as Julia Carpenter. (Yes, she also has some telepathy-based powers.)
Now, while this saga is following the 2015 Secret Wars, I would be remiss if I didn't include that Peter Parker theorised that the alien symbiote mimicked his memories of Julia Carpenter's suit, which he saw during Secret Wars (1984). The symbiote is still someone in the 616 universe.
Marvel does misdirect us all the time. We've not actually seen any footage of Sadie Sink, and we've also not seen any footage of the main villain, not that there has to be one.
Also, to pre-empt the entire "MCU wouldn't use female Spider-Man characters after Madame Web" argument, the MCU never stopped using Spider-Man villains after the failures of Morbius and Kraven the Hunter.
Now, the only valid reason I can see for Jean Grey would be as a Secret Wars MacGuffin. If you don't know, when Doom creates Latverion, all the inhabitants he brings in through the Beyonders' power have their memories of their previous worlds wiped, with only Doom, Strange, and Molecule Man remembering. Jean could play the role of awakening people on Battleworld to the truth. The only other people who know the truth are the people on the liferaft who crashed on Battleworld after it was formed.
Now, the only other extremely wild theory is something that happens regularly during the Secret Wars tie-ins: that this movie isn't set on Earth-616, but on another Earth. The Secret Wars tie-in Spider-Island doesn't follow 616 Peter. Planet Hulk follows Steve Rogers, and I don't mean Gladiator Steve Rogers. I mean the Hulk that we don't actually find out until the end is the real Steve Rogers from an Earth where the super-soldier program used gamma radiation to transform Steve.
If that's the case, then I would definitely be saying it's Jean Grey, as Secret Wars ends with different Earths merging. It's how Miles moves to 616. Since both the Fantastic Four and the X-Men don't exist on MCU 616, it makes sense that this is how they will end up on 616 after the soft reboot. So, having established X-Men characters from another world before Secret Wars would make a lot of sense.
Remember, in the Multiverse there are infinite Earths that can follow similar storylines despite being different Earths. Agents of S.H.I.E.L.D. is an example of that, as they ended up on a branched timeline due to time travel where the world was completely destroyed.
But I want to know how you would feel if, by the end of the movie, we found out that it's set on another Earth that ends with an incursion.