We know next to nothing about what this movie will be about as I think the story will heavily bounce off of The Kang Dynasty. That said, we know about the comics and the scale of it has me both worried and extremely excited.
Secret Wars is going to be absolutely HUGE and the cameos/final battle should be ridiculous. I'm thinking we could see pretty much everything there is to see. Possibilities include Chris Evans fighting himself as two different characters, RDJ gets back in the suit one last time, Wesley Snipes as Blade, name any of the Fox X-Men and they’re fair game, Lou Ferigno as The Hulk, Ben Affleck as Daredevil, Jennifer Garner as Elektra, Nic Cage as Ghost Rider, Thomas Jane as The Punisher, Anything in the Sony Spider-Man Universe, Matt Salinger as Captain America, Scott Paulin as Red Skull, David Hasselhoff as Nick Fury, etc.
Think of how many freaking Marvel movies have been made, especially the cheesy ones before the 2000's when they were struggling financially. There's such a deep bench of characters within the multiverse to pull from that if they actually pull it all together, it'll make the shock and awe of NWH seem like what I think they want it to feel like, which is an appetizer for what's to come.