Unlikely to ever happen in the Crysis franchise at least, but I've always wanted the nanosuit player to get sent back in time for whatever reason and look at the faces of people from back then when tin man uncloaks
.
Obviously not as a user-made mod, but a real story by the devs. It sounds like it would be possible, since the Ceph are very advanced and all, and their last chance would be time-travel.