I think he should have a sort of Love Triangle. Not so there is the drama of juggling two girls or one finding out or something. Not that type of triangle. It should be Agent Sharon Carter of SHIELD and Bernie Rosenthal, an stained glass artist and glass blower.
The idea would be that he is drawn to both women, one represents his life as Captain America and the other represents his life as Steve Rogers. Which should he choose?
It would help symbolize the choice Steve feels like he has to make, being Steve or being Captain America.
Thats what I would make the movie about too.
It would take place in modern day and show how Steve is struggling with his new life. Should he give up being Steve since everyone he knew is dead or dying? Should he just be Captain America? Or should he try being Steve? Being an artist like he was before the serum and WWII? Should he try to have a normal life apart from Captain America?