While I have some time, let me lay out why I think Affleck is the front runner.
1. Ben Affleck is a really good director. Gone Baby Gone and The Town got great reviews. Argo has early awards buzz. In addition, not only were Gone Baby Gone and The Town well reviewed, they were gritty crime drama/thrillers which fits in well with with the established aesthetic of the Nolan franchise. WB will certainly prefer an acclaimed director with similar credentials to Nolan if for no other reason than to make it look like it's not a step down for the franchise.
2. WB has backed Affleck's last two films The Town and Argo. While it's not a deal breaker, I believe it would be WB's preference to work with a director who already has a good working relationship with the company. If nothing else, it's probably better for the morale of employees if WB promotes from within to head up one of their prize franchises rather than basically say no one in the company is good enough.
3. Ben Affleck is in his directing prime. Obviously WB isn't going to hand Batman off to some unproven director. I also don't believe they're going to hand off the franchise to an older director that might not have much gas left in the tank. A youngish director that can see Batman through for the next decade is certainly on WB's wish list.
4. Ben Affleck has no other major franchise commitments. If WB is going to hand off one of their prime franchises, they're likely to hand it off to someone with no other major commitments/distractions on his plate.
5. Affleck has legit comic book cred. It's not an essential, but it certainly doesn't hurt.
6. Accidentally or not, WB has already linked Nolan and Affleck by putting the trailer to The Town in front of Inception. Considering Argo is one of WB's biggest releases between The Dark Knight Rises and The Hobbit, a trailer to Argo in front of The Dark Knight Rises seems likely. If Argo is as good as early buzz suggests, Nolan and Affleck might be further linked together through awards season buzz. That would make an easy transition for WB when they are ready to make an announcement. Affleck and Nolan apparently already have something of a relationship with Affleck being offered Superman at one point and turning it down.
I don't necessarily think it's a given that it's going to be Affleck, but I think the next director of Batman is going to have a similar set of qualifications.