Not sure how many people make use of this feature, but it's been traditionally something Rarity tracks for each expansion.

Roadmap:

• Add achievement-related NPCs in the Options module
  • https://www.wowhead.com/achievement=40435/adventurer-of-the-isle-of-dorn
  • https://www.wowhead.com/achievement=40837/adventurer-of-the-ringing-deeps
  • https://www.wowhead.com/achievement=40840/adventurer-of-azj-kahet
  • https://www.wowhead.com/achievement=40851/adventurer-of-hallowfall