That is an interesting comment if you think about it. What did he mean by skull? Could he have meant Johann Schmidt, The Red Skull, who we last saw in Captain America: The First Avenger? At the end of that movie, The Red Skull grabs the Tesseract and appears to disintergrate. Yet future films have determined that the Tesseract is in fact the Space Stone, one of the notorious Infinity Gems Thanos is looking for. With the Marvel Cinematic Universe now filled with many galaxies and even a multiverse to inhabit, The Red Skull could indeed have transported to safety in the moments before the plane he was flying crashed into the ocean.
The only wrench in the works is the fact that the actor who played The Red Skull in the movie, Hugo Weaving, has gone on record stating he did not have a good time working on Captain America: The First Avenger. While time has apparently made his heart grow fonder on the role, wearing the amount of makeup needed to make him look like The Red Skull would make even the most eager of actors take pause.
Yet thanks to Doctor Strange, the multiverse allows the Marvel team to bring back characters without having to bring back the orignal actors playing them. The Red Skull they bring back doesn’t even have to know the Steve Rogers we’re familiar with in the films. With reports that Chris Evans’ contract will be up after the filming of Avengers: Infinity War, Phase Four of the Marvel Cinematic Universe could see the introduction of new versions of these characters. Marvel Studios has a lot of directions they can go with this if Samuel L. Jackson indeed let the actions of Nick Fury slip.