I'd love to see an implementation of an enemy database with increasing levels of unlock. For example, Kill 10x of "X enemy" unlock basic data, kill 100x of "X enemy" unlock detailed stats....etc. To know what the potential drop rates and drop items for enemy rarity would also be nice.
Also within that database/journal, an enemy locator would also be helpful. To know which floor or floors certain enemies would appear with percentages of rarity appearance.
Since there is "Armor Pen" and "Flat Armor" knowing which stats to improve based on enemy capabilities would help with planning.