In FFXII, you
unlock a tiny bit of lore about an enemy if you kill enough of it's kind.
Example:
FFXIII did similar with DataLogs,
although this was more focused on the characters and world than it was the beasts.
I'd love for something similar to the above to be added to FFXIV. We already know that Encylopedia Eorzea gives this information (got them both and
love them), but I'd adore a gameplay aspect to it. It'd really give more reason to actually go around killing the various monsters in the game, encouraging more participation in duties, FATEs, the lot. Given that the Encyclopedia means such information already exists, this would mean that the only thing that would be needed to add to the game is the gameplay element of unlocking them.
I'm not against the idea of having less information than is in the Encyclopedias either, just to ensure that they still hold their prestige, but we all know that they are finite in stock and often aren't available for years. It'd be really nice to have this as an in-game feature to add a simple yet lengthy exercise of 'crafting' the Encylopedia in the game for an NPC who writes it, or something, and we keep the information in a Log for our own perusal should we wish. It would also give in-game lore to Encylopedia Eorzea's creation!