Terminator Salvation

[Roogle]

I'm guessing there will be no Arnold butt in this one?

I am not sure what will happen. Wikipedia had the following to say on the subject:

Roland Kickinger as the prototype T-800: This will be the first Terminator film in which Arnold Schwarzenegger does not play the Model 101 Terminator, because he is serving as Governor of California.[21] The Austrian-born Kickinger previously portrayed Schwarzenegger in a 2005 biographical film on the A&E Network. When asked about his role, Kickinger said it's "Arnold's character in the first Terminator. That's basically my role, but 20 years before, so it establishes how the Terminator [came] about." He also revealed that there is a "very strong scene in the film where John Connor for the first time meets the Terminator, and he doesn't know if he's a good guy or a bad guy."[22] Polish strongman athlete Mariusz Pudzianowski was also considered for the role.[23] Schwarzenegger visited the set, leading to rumors he was providing his voice and got scanned for a digital double, which would be mapped onto Kickinger's physique. He had granted the Halcyon Company permission to use his likeness in the film.[24] McG would only admit "We're trying to synthesize a human character with a CGI character and that may or may not have something to do with the T-800."[25]