My big question about a Ki power source is what else can you do besides Monk? Some suggest Ninja, but I'm not sure how that isn't martial or potentially shadow? What other classes can you put into this power source and how do they work?
I know they already said something about it, but I think ditching the Ki class and reflavoring the monk (whatever role) as Martial wouldn't bug me too much unless I'm shown the light about what Ki really means.
Ki works as something that is a lot like Martial (as in it is heavily linked to training and weapon use), but much, much more flashy. Where a Martial character would use strength, technique, and strategy in order to deliver a solid blow with a sword, a Ki character would move faster than the blink of an eye and release an energy shockwave from a sword instead. Basically, Ki is Martial with added energy blasts and the plausibility limiters removed. For example, I don't think there is a single Martial class (or even a class at all) that has a Close Blast 5
Weapon power, but such an attack would be fairly normal for a Ki character, especially if WotC was serious about emulating Hong Kong martial arts films and Japanese videogames and anime.
As for classes...
The Ninja is not going to be Martial simply because it would be impossible to differentiate it from the Rogue in such a role. The Rogue is already stealthy enough, can pull off a ninja vanishing trick, can double jump, and gets a bonus for using shuriken, after all.
If we are going to see a dedicated Ninja class, it is probably going to be much more fantastic (and probably would involve breathing fire, walking on water, illusions, and summoning giant frogs). If anything, I am hoping that the Ninja is going to be Elemental, rather than Ki, because I don't think it is necessarily a good match for Ki.
I can easily imagine a Ki Swordsage/Samurai class, built around high-speed movement, iaijutsu attacks, blade shockwaves, area-effect sword attacks (like the previously mentioned Close Blast 5 Weapon power), and other such flashy and over-the-top feats often associated with characters of folklore and anime.
Honestly, I think they could probably create a fairly respectable number of classes simply by elaborating a number of different supernatural fighting styles, and bringing them together based on concept. For example, a pure barehanded "Monk" class that uses throws and Ki-blasts, a more weapon focused "monk" class that uses staff and spear-based fighting techniques (give it more of a Chinese/Romance of the Three Kingdoms flair, possibly), a "dancer" that uses unusual weapons like fans and light weapons like knifes in order to confuse opponents, a class that can debilitate a foe with a single touch, etc. So long as these classes are distinct and have a supernatural edge, they can be very different from Martial classes and remain quite unique.
Actually, another good class that could easily be Ki is the old 3.5E Soulknife class. It was never a great fit for psionics, but I think it would work with Ki very well.
