Though viewers seem to be more than satisfied with Captain America: Civil War, many comic fans were disappointed with how far Zemo seems to be from his comic counterpart. Though Helmut Zemo of the comics was affiliated with Hydra and grew up a Nazi, his on-screen version seemed to be purely driven by revenge. But that may not be all there is to him.
In one of the most overlooked lines of the movie, Zemo speaks to Cap in person for the first time. He tells Cap that he knows everything about him, except one small detail... a hint of green in his eyes. A small imperfection, because they're not pure blue. It may not have been obvious, but it makes one thing abundantly clear.
Helmut Zemo is still a Nazi in the MCU.
Zemo mocked Cap for what he perceived as an imperfection that removed him from the Aryan "master race" of Nazi idealism. If Zemo returns, it's highly likely this will be expanded upon, whether he's with the Thunderbolts, Masters of Evil, or on his own. It's definitely a small detail, but it betrays a whole lot of potential depth that has yet to be tapped.
It also shows that the Russo brothers and the studio didn't fully step away from his comic origins. It seems unlikely that they'll leave the character where he is for too long. Zemo may finally be the well-developed villain Marvel fan have been hoping for.