Im sure we all kind of see where Nolan likes to work with the some of the same actors again for new movies, below are the people Id think hed cast for a Fantastic 4 movie.
Mr Fantastic
Christian Bale
Invisible Woman
Marion Cotillard
Human Torch
Joshep Gordon-Levitt
The Thing
Tom Hardy
Dr. Doom
Cillian Murphy
Well Nolan, even though you will never see this post or do an F4 movie, here ya go :)