Initial proposal:
Learn from the Ancients

Instant
Draw three cards, then discard two cards unless you discard a creature card.
Having begun to play around with a Riku led Commander deck, I'm surprised a card like this doesn't exist. Would this be too powerful? The only potential area of abuse I see is (Legacy) Reanimator, or Sneak, NOrder, and Show (which may want to discard Prog or Emrakul etc).
With a more restrictive mana cost than Thirst I think this is probably fine, but playable in Legacy, unplayable in Vintage, and great for Commander.
Most current version:
Learn from the Ancients

Instant
Draw three cards, then discard two cards unless you discard a creature card.