I kind of like the idea that a species can be exterminated. It brings a more realistic approach to random battles. I remember in older games when I would grind and think "could there really be a never ending amount of imps in this forest?". Than again, I appreciate those fantasy aspects of it so it's not a complaint.

Maybe there will be some sort of goal in extermination. Kind of like how in Final Fantasy X, you could try to get 10 of every creature for the battle arena.