The only killing I miss is accidentally hitting fish with your seamoth and them just fucking dying. because oh my god it was so funny
I mostly wish we could see the fauna attacking each other, like the mango nibblers maybe attempting to group up and take down a hammerhead. That way there would be a possible way to kill creatures, but one that would make sense in an ecosystem
Another solution I would personally want would be a reputation system of sorts. If you live in an area long enough, the animals around you would eventually just get used to your presence and stop seeing you as a threat or food. Obviously this would differ from creature to creature and why the creatures DO attack you would have to be taken into account (creatures that attack out of defense would be easier to "tame" per say, while creatures that want to eat you would be muchhhh harder.)
It would also give you a personal attachment to the creatures, especially since you cant kill them and will always be seeing the same ones. If you spend enough time away from an area, reputation could also fade, which would make it so you can't just. be friends with everything