Kevin Feige recently chatted with IGN regarding the possibility of the Mandarin (the real Mandarin) actually being revealed and the Red Skull returning. Things sound pretty good, especially with the Mandarin and the one shot they did as he said:
“There have been [talks]. That’s one of the reasons we wanted to do the fun short that Drew Pearce wrote and directed. That was to clarify, ‘Hey, just because we did this thing doesn’t mean this other thing doesn’t exist.’ And as we were making Iron Man 3 — and I think Drew’s spoken about this — that was always our intention, was that Aldrich Killian was perverting the notion of these things he’s heard.”
As for the Red Skull making a return, it appears that it could go either way. On why they made his “death” in Captain America: The First Avenger the way they did, he added:
“Well, the way we showed his ‘demise’ in The First Avenger was to showcase to people that he could perhaps pop up again sometime. I honestly don’t know when or where that would be.”
While it might be to large for the show, perhaps we could see Red Skull pop up in Agents of S.H.I.E.L.D. considering their current priority of dismantling Hyrda. Only time will till for both, but it does sound like a matter of when and not if.