4e Player's Handbook, page 54 wrote:Other Power Sources: Additional power sources and techniques provide characters of different classes with powers and abilities. These will appear in future Player’s Handbook volumes. For example, barbarians and druids draw on the primal forces of nature, monks harness the power of their soul energy (or ki), and psions call upon the mind to generate psionic powers. Future power sources include elemental, ki, primal, psionic, and shadow.
They dumped Ki and Elemental before printing a single class for them. Which in the case of "Ki" is because people were actually angry that they attempted to make some classes get the "Asian" power source, on the grounds that that is totally racist. Which of course, it is.
Now there were a number of problems with the way they handled it, over and above having "Asian" as a list item for where your powers come from. For starters the power sources didn't
do anything. A guy swings his sword so hard that the target
catches on fire, is he a Swordmage (Arcane), Psionic Warrior (Psionic), Barbarian (Primal), Blackguard (Shadow), Paladin (Divine) or just a Fighter (Martial) who happens to have a sword that does that on its own? The fact is, from that description, you have no idea. And since 4e is completely bereft of setting or character elements that would give you more information, that's that. And since nothing really
interacts with those power sources in any way, it doesn't even matter.
The second problem was that the first book to come out was "Martial Power", that just gave a bunch of options and power creep to Fighters, Rogues, and Rangers. This meant that right away, any new power sources (and even any new classes in the power sources they already had) were by definition thin and weak. Unless they came equipped with an exploit people would complain about, they were a priori worse than what was already available.
And the third problem was that they just never delivered the kind of classplosion that that kind of categorization would justify. The fact is that they had 4 "roles" and every single power source should have been fleshed out to have more than one class for each role. Right away. There should have been 35 classes in the first year. Considering how procedurally generatable 4e content is, that wouldn't even be hard.
-Username17