This is what they had to say when asked about relationships to be explored in Infinity War:
Joe Russo: Certainly Scarlet Witch and Vision. Its a very compelling story. Obviously, its one ripped from the comics that, for many years, there was some very interesting storytelling and characters. One character is searching for how to identify with humanity, another who is on a journey away from her humanity towards becoming a very powerful being.
Anthony Russo: I would also say Captain America and Iron Man is central. Can those guys ever repair their relationship? What is their relationship ever going to be like moving forward from this?
Joe Russo: Should they repair it?
Anthony Russo: Thats as complicated as anything. The other relationship thats still exciting to us is, again, Cap and Bucky. The wonderful thing about this movie, which started in Winter Soldier, is that Cap had a belief in him, that theres still a human being inside the Winter Soldier that he can save and that he can reach, and hes gone to incredible lengths now, with incredible faith, that thats waiting for him if he goes there. Hes found that human being inside Bucky Barnes, but who is that guy going forward? Just because hes found and hes there, hes still this crazy, bastard hybrid of who he used to be in The First Avenger and this killing machine.
Joe Russo: If hes not Bucky Barnes or The Winter Soldier, then who he is?
Anthony Russo: Hes somebody new now. What kind of relationship will him and Cap have moving forward?
And Steve is probably not going to make it out of Phase 3 alive, so yeah, I'd say Sharon's chance at the spotlight has passed.