I don't think we've been told anything about it yet.

IMO, I think it can add some flavour to a game if done well - the way characters react to you being dependent on it - but then there's the question of what it would mean for the in-world mechanics.

Would a karma system imply that overnight, your character somehow becomes so well-known that their actions precede them wherever they go, which is why NPCs would react to you a certain way right in your very first interaction with them? It can feel quite jarring to have a character who just feels like a regular guy, and then you meet a group of people who hate you already because you've been acting like an asshole in a small town fifty miles away. How'd they know what sort of person you are if they've never met you before?

I don't think I'd miss it if it wasn't included, as long as there are other ways to affect the way NPCs see you, not counting faction loyalty.