Board Thread:General Discussion/@comment-167.135.254.225-20140516213320/@comment-733050-20140516221954

Christopher Markus and Stephen McFeely told Den of Geek or some other interviewer that they intentionally left Red Skull out of Winter Soldier for the third film. If you've read the thirty or so issues by Ed Brubaker that the films are based on, you'd remember Skull was dead for the first dozen issues and is only revealed to be alive again after Bucky regains his memories.