Red Skull

The fans have been saying that the Red Skull would return since The First Avenger concluded. The character wasn't explored to his full potential, and the way in which he was eliminated was more than ambiguous. So even if Hugo Weaving doesn’t return to the role, the door needs to be opened once again. After all, the Tesseract functions like a literal one "“ what if Zemo found a way to bring the Red Skull back?

Even more, maybe he has already done it and maybe, right now, the Red Skull is in that stasis tube regenerating (after all, a huge explosion and instantaneous travel to the other side of the universe would surely leave some marks).

So maybe Zemo’s role in the Civil War is to usher in Captain America's greatest enemy, the founder of HYDRA, and the one who can orchestrate a war between Earth's mightiest heroes from behind the scenes.

But we won't bet on that. Tony Stark would have no reason to let the Red Skull wage war once again on Earth.