Become The New Red Skull
The last time fans saw someone take the super-soldier serum, resulting in homicidal behavior similar to what was seen in the fourth installment of The Falcon and the Winter Soldier (that wasn’t involving Bucky as the infamous Captain America nemesis), was the case of The Red Skull. This crimson-headed psychopath took the serum as well, and it did not turn him into a hero by any means.
Dr. Erskine told Steve back in Captain America: The First Avenger that the serum will make a good man great, so if it’s taken by an evil son of a gun, things will not end well. While Walker may not have the same expertise and experience The Red Skull had, he could very well become a new modified version of the dreaded Marvel villain.
As his time in the service and time as Captain America have only resulted in loss and pain with no significant change occurring, Walker may find answers in Hydra’s manifesto and come to terms with the notion that the nefarious organization’s ideals may be the only way to ensure the madness ends. While it may seem wild, it’s completely within the realm of possibility that he could very well become the new Red Skull to be the new rival for Sam Wilson’s Captain America after The Falcon and The Winter Soldier.