I see this being like GOTG, where Yellowjacket is in the Ronan role and Kang is in the Thanos role, though perhaps a little larger.
I could see it playing as Augustine Cross didn't get blipped and took control of the company during the 5 Year Gap (potentially with help from OsCorp, if they do indeed get introduced in FFH). Maybe he gets Bill Foster and Ghost to help him. He found out about what happened to his dad and now that Hank & Janet are back, kidnaps them to force them to help him look for him in the Quantum Realm - Cue QuantuMania: A 'Life Aquatic' type voyage into the Quantum Realm with our heroes, their captors, perhaps the Ex-Cons and Foster + Ghost, maybe Cassie (so she can become Stature/Stinger). A culmination of everything in the last two films.
Christopher Mintz-Plasse as Augustine Cross
Thomas Jane as William Cross/Crossfire