IMO dual spec, or multi-spec is a necessity in games nowadays since the majority of the playerbase is comprised of the the wow revolution and the classes are designed as such. [ie each AC is one of the following: tank/dps, dps/heal, ranged dps/melee dps hybrids]
Again IMO, EQ1 had the right idea with class design. A huge variety in classes along with an additional leveling mechanism that allowed you to constantly improve your character. Points were not wasted as, if you put in the time, you could get everything eventually. Abilities were based on the class, not the skill/talent/AA choices.
Like the majority here, I'm hoping this core feature does is not legacy level/credit restrictive.