I was messing around on google and found this story arc of Captain America. Marvel wikia's recap: A soldier named Frank Simpson was a soldier in Vietnam. He was given steroid drugs and augmented with cybernetic implants. This caused him to go insane. He fought in Vietnam's most dangerous battles as Captain America for five years. During that time he had the American Flag tattooed on his face. This kinda showed folks how crazy he was. Frank defected in 1972 and was not seen again until the early 21st century, not too soon before the return of Steve Rogers.
Frank was selling his blood to America's enemies. North Korea is the case when S.H.I.E.L.D. tasked Steve and some British S.A.S. men to investigate. Steve engages Frank, but looses. Soon after that, he tracks Frank to a Cambodian village. Frank injected the villagers with his blood so basically Steve had to fight a whole village of super soldiers. When the villagers finally beat Steve, he was imprisoned.
I know this will not be Captain America 3. This probably won't make it into the MCU, but I think this could make a great movie. Marvel would have to pay Chris Evans more than they do RDJ to make him stay in the MCU. Should Evans end up staying, this would make a good Cap 4. What do you guys think? Let me know below!