I think the idea of shots that can cripple based on zone damage is a terrible one.
If the biggest challenge in the whole game, fighting a major dragon, came down to simply practicing a single shot that makes the fight a win, or easily winnable, then the game has no real challenge.
No, if I could wander through any given cave or dungeon and cripple the enemies by a first shot to the head or ankle, the game would become boring or repetitive.
But surely the armour they are wearing (or natural armour) combined with the fact that enemies aren't leveled like they were in OB would make this better? I'd rather have decent locational damage than being able to spam arrows to an unprotected limb with no real difference, or indication that they've been affected by the damage.
They could also make it so that different dragons had different weak spots, so some had an unprotected belly, head, limbs, wings etc. depending on their attack style (where they would try to protect their own weaknesses). Or if not, the fact that dragons are pretty badass anyway could stop them from getting a crippled limb from one lone blow anyway.