We already know that Jason Clarke (Zero Dark Thirty) is set as John Connor, with Emilia Clarke (Game Of Thrones) as his mother Sarah, Jai Courtney (Jack Reacher) as Kyle Reese, Day Okeniyi (The Hunger Games) as Danny Dyson and Arnold Schwarzenegger returning as the Terminator. This pretty much covers the original line-up set, which potentially means a new role for Smith. The studio press release also adds that he has a "strong connection to John Connor".
Introducing a major new character is arguably a good thing. After all, if you're going to reinvent something, you might as well add something new to the mix in the process. If we were guessing, we might speculate that Smith could play, or at least become, a new antagonist for the series.
Terminator: Genesis hits UK screens on 26 June 2015.