I don't care for John Cena, and he doesn't seem very popular as far as big budget blockbusters go. Isn't he in a lot of straight to DVD/redbox movies? I don't feel like he has the acting chops to pull it off. I think that would be going a step in the wrong direction personally.
Yeah I agree, Arnold was great in genisys, the films shortcomings had nothing to do with him.
Needing Acting chops to play a killing emotionless robot....