The description given by Deadline is: "Redford is in talks to play a senior leadership role in S.H.I.E.L.D., the superhero collective run by Samuel L. Jacksons Nick Fury character." That, to me, implies that the character isn't an active agent but may have been one prior to moving up the SHIELD food chain. So perhaps it could be Clay Quartermain, if they change the character's origin so that he was one of the original agents of SHIELD when it first began. Perhaps he could be a colleague of Peggy Carter's from when she ran SHIELD. That would be a kick in the head for Steve, I think.