Honestly, George Clooney would fit nicely in the role. As for Illya, I wouldn't mind a woman taking on the character.. Milla would be fun, in a no-nonesense, guns and glory kind of character.
There was a Clooney version with Steven Soderbergh that never got very far. Hell, there's a good chance this might not even happen with Tom Cruise. Actors are attached to projects and leave all the time.
That's how Green Hornet went from George Clooney to Greg Kinnear to... Seth Rogen.