Though no elements of the story have been leaked, the casting allows for much speculation, as many of the characters that should be dead by now, are suddenly alive and kicking. This could indicate that we likely to see a Terminator film that is equally split between the present and the future. This could also mean we are heading away from the 'future is now' Terminator Salvation premise and returning to the deadlock draw that allows us to have sequel upon sequel. Dawn of the Planet of The Apes' Jason Clarke must be representing scenes set in the future as he will be playing a very middle aged John Connor.
"Miles Dyson's young son, remember him? He was present when Sarah Connor attempted to assassinate his father in Judgement Day, now a young man he will be played by actor Dayo Okeniyi."
Looking at the rest of the cast; we can see that Game of Thrones' Emilia Clarke is playing a young Sarah Connor, which could mean that we are returning to her initial encounter with the Terminator sent to kill her. It might also mean that the teenage/young man - John Connor seen in T2 may not feature...unless this is where Percy Jackson's Cyclops actor Douglas Smith comes in to show us a latter stage in the timeline.
Arnie of course will be playing a Terminator, but who's side he'll be on is still up for debate. Plus there is another Terminator in the mix, a T-800 version in the form of Aaron Williamson. Williamson a former Marine, comes with a body that shows us with no uncertainty why he got the role and why he'll be lethal!
Courtney B. Vance will be playing Miles Dyson - the Cyberdyne Systems engineer that will invent the micro-processing chip that kick-starts the entire saga...and yes he did die in Terminator 2: Judgement Day, so like I suggested, a re-boot may be upon us. Also spun into the narrative will be Miles Dyson's young son, remember him? He was present when Sarah Connor attempted to assassinate his father in Judgement Day, now a young man he will be played by actor Dayo Okeniyi.
As for the rest of the story I imagine it's a waiting game but I predict 3 points of focus on the timeline:
1: THE PAST - A young Sarah Connor comes across the Terminator for the first time and is protected by Kyle Reese (played here by Jai Courtney) sent back by John Connor.
2. THE PRESENT - The teenage/early manhood years of John Connor; we see him learning all he needs to, in order to become the leader he does.
3. THE FUTURE - The computers have initiated Judgement Day, but due to events in the timeline potentially having been changed, the story in T3: Rise of the Machines and Terminator: Salvation have a new tapestry of events to be woven on top of what now doesn't exist?.
With the time travel anomalies that could to be flying around, I believe anything can happen in the upcoming films. Anything can be subject to change, to be reset, erased or be completely terminated from the timeline.