Why would the kerambit be a favored weapon of ninja when it is a weapon for Southeast Asia and the Philippines? Well, I suppose that there might be some overlap, since most "traditional weapons" that get associated with ninjas, such as sais or nunchucks, tend to originate in Okinawa, which is at the southernmost part of Japan. (complete tangent: I found while using wikipedia for this subject that there is a traditional Okinawan short sword and shield style. The references actually has a website with a picture of an old dojo master using a turtle shell as a shield. Just thought I'd share that)
I know that you can't entirely apply real world geography to the game, but heck, the devs kind of did that anyway in their creation of the various nations, particularly with the various Asian stand-ins that get ninjas and samurai.
Anyway, besides a few additions that could be made here or there, the current system of simple, martial, and exotic weapons typically work for most items. The only time I can remember a major weapon proficiency update was the addition of brassknuckles, the cestus, and temple swords to monks, and that was only done in order to make them more viable at the time. Ninjas and rogues work just fine as of now (well, you get arguments about that, but that is more open for debate)
There is no need and it won't happen, Paizo doesn't change the Core Rules to reflect new content,
it's supposed to stand on it's own and they've stated they don't plan on doing that sort of thing.
What is confusing about Knife Master not mentioning anything about proficiency? Rogues already have proficiency in Daggers. The Class Abilities CAN work with exotic weapons, but you don't need them to get 100% usage out of the abilities.
Most of the new 'exotic' weapons could really just use existing non-exotic stats anyways, so using weapon stats you have proficiency in isn't a big deal IMHO.
The Knife Master does not gain additional proficiencies.
Just as a Monk is not proficient with all weapons with the Monk feature, there are weapons that will work with a class feature, but the class itself will not grant proficiency with it.
This is not a mistake.
If a new weapon is presented, and it is intended that a class be proficient with it, then it note so in the weapon description.