Class specific quests where completing them adds an additional point (and maybe max skill point) in a particular skill that is considered useful to that character.
Eg. Barbarian completes quest, Whirlwind now has 21 skill points, and you now have an extra point in it
Wizard completes quest, Chain Lightening (or Electrocute) now has 16 points and you now have an extra point in it
Can encourage people to experiment the rune system with different skill, whilst not wasting any "skill points" per se.
These quests would then be discovered, and people could make builds from the beginning based on what skills get the extra points (despite the game being more tactically and gameplay focused than just numbers)