there would be almost definitely NOT be 3rd person option. And before you guys start shouting, this is based on what the devs have released. An ability which has been revealed by the devs is Sense Of Perspective, basicly gives you a 3rd person view when completing objectives so you can see your surroundings, so if the entire game was 3rd person wouldn't that defeat the entire purpose of that ability? Of course these are subject to change so thats why I said 'almost'.
Replays are of course a completely different matter
That is where 3rd person perspective could be well used. Other than that, there is still far too much to be done to make it work well. The coding involved to have the camera follow you around in 3rd person perspective would just be ridiculous. There would be so many moments where you were jumping around, over, and through obstacles that completely block you're camera angle. I'm sorry, but no, I don't want that [censored] stuff happening while I'm chasing/being chased.
As for replays, it would be quite awesome to have something similar to the MW2 game winning kill cams (for every death) that zoom in on my character as the death dealing shot is delivered. Those moments where I got killed mid-jump would be great to watch in slow motion. Plus, that would give me a chance to see my personal bada$$ dying in an awesome way.