They should let you kill enough wild pokemon in the next game so that you can ACTUALLY make it's species go extinct in your game (you'd have to trade for it again, breed it, release it to repopulate). Now THAT would be a fun dynamic. You could let them breed like crazy and have them swarm everywhere and destroy other pokemon's habitats, or you can kill them all. It would make it a lot easier to catch those low rate pokemon in the wild as well!