I want them in X5.
Death - Archangel (definitely Foster)
The rest, I'm not sure. I've thought about Wolverine (yes, our hero from the last 3 movies) slowing changing in the next 2 movies until he turns bad and joins as War. I know he was Death in the comics, but we've already got Archangel to fill that role.
Famine and Pestilence should be characters taken from the comics who haven't had a real role in the movies yet. I don't know who, except probably NOT Sunfire. I'll be killing off Pyro with the Legacy Virus in my X5 and giving Rogue his powers. We don't need that much Pyro action AND another fire-manipulator introduced.