There was a possibility, I suppose, that Arnold Schwarzenegger would have a human role in the next Terminator movie. He has, after all, a slightly different appearance these days than when he shot the third film, more so the second.
And most definitely the first.
Given that Terminators are assumed not to age, it seemed a reasonable punt that he might get the kind of role Lance Henriksen took in Alien 3, a human model for the robot we're familiar with.
But now Arnie himself has said it's not so. Talking to The Arnold Fans, Schwarzenegger has confirmed that he'll be playing The Terminator itself:
I'm very happy that the studios want me to be in Terminator 5 and to star as the Terminator, which we start shooting in January.
January's soon, but it'll be a year since we broke the news he'll be in the movie. We didn't know who or what as, but we knew he'd be in there.
The last Terminator film used a CG likeness of Schwarzenegger to play a T-800. It seems likely that they're planning a variant on this trick for the next entry. Maybe he'll play the role through motion capture, or maybe he'll just be super digitally airbrushed.
Paramount are currently negotiating a deal to distribute the new Terminator movie. AnnaPurna films are financing and producing, with the script written sometime James Cameron collaborator Laeta Kalogridis and Drive Angry's Patrick Lussier. I'm half expecting Lussier to be announced as director – and possibly soon if production is going to start in January.