My guess is SNK is already working on KOF XIV, though.
Highly doubt it. I don't think they're gonna get to it anytime soon.
It wouldn't make sense for SNK to pay their developers to do nothing. Either they've shut down their gaming division, or they're paying them to do something.
We haven't heard anything about their gaming division closing, so the logical conclusion is that they're working on something.
KOF XIII was a success for SNKP. Now, there are several ways to build off a successful game. They could use the experience and talent to bring back another (less popular) IP, like Fatal Fury, Metal Slug or Samurai Shodown. This is somewhat risky. They could use the experience and talent to create a NEW IP. This is even riskier. Or, they could simply make a sequel to their successful game. This is the safest option.
Given SNKP's history, I'm guessing (just a hunch) that they're going with the safest option.
All in all, I'm pretty confident XIV is already in the works. But it may be a while before we hear about it.