Sources should be broad groups that do not encompass very specific niches. For instance Ki and Psionic should be together, bardic music, elemental, illusion, and arcane magic should be together, artifice and martial should be together, and divine and philosophical sources could be together too.
The ones that I can see as the most likely to be added would be:
Psionic: telekinesis, telepathy, and body control
Shadowfell: necromancy, shadow magic, warlock aspect etc
Feywild: druid, animal shapechanging, warlock aspect etc
infernal (arcane): warlock aspect probably not a power source in of itself.